Antimutagenic compositions for treatment and prevention of photodamage to skin

ABSTRACT

A method of improving DNA repair and reducing DNA damage and for reducing mutation frequency in skin for the purpose of reducing consequences of exposure to solar or ultraviolet radiation is disclosed. The methods comprise administering to the skin a composition containing deoxyribonucleosides in concentrations sufficient to enhance DNA repair or reduce mutation frequency in a vehicle capable of delivering effective amounts of deoxyribonucleosides to the necessary skin cells.

[0001] This application is a continuation-in-part of U.S. applicationSer. No. 08/963831 filed Nov. 4, 1997, herein incorporated by reference.

FIELD OF THE INVENTION

[0002] This invention relates generally to treatment and prevention ofphotodamage, genetic damage, and tumorigenesis in skin and other tissuescaused by exposure to solar or ultraviolet radiation or other mutagens,comprising administration of deoxyribonucleosides or esters ofdeoxyribonucleosides to a mammal such as a human. These compounds arecapable of reducing DNA damage, mutation frequency, and tumorigenesiswhen applied topically before, during, or after exposure to mutagenicradiation or chemical mutagens.

BACKGROUND OF THE INVENTION

[0003] Exposure of skin to ultraviolet (or ionizing) radiation damagesDNA, which if unrepaired or improperly repaired, can lead tocarcinogenesis as well as contribute to acceleration of the agingprocess. DNA damage and consequent genomic instability are definingcharacteristics of both carcinogenesis and biological aging. Patientswith defective DNA repair capabilities in diseases like xerodermapigmentosa display premature skin aging and a very high incidence ofskin cancers (Robbins and Moshell, J. Inv. Dermatol., 73:102-107, 1979)on sun-exposed areas of the skin. Pharmacological intervention in damageto skin due to solar or ultraviolet radiation has heretofore beenlargely restricted to agents like sunscreens or free-radical scavengersintended to prevent damage, or agents like retinoic acid or glycolicacid which are intended to remodel the surface of radiation-damaged skinwithout necessarily addressing the most fundamental mechanisms of cellor tissue damage and repair at the level of genomic integrity.

[0004] In practice, preventive measures like sunscreen use are notcompletely effective, and exposure to sunlight is not alwaysanticipated. The incidence of skin cancers in the United Statesapproaches 1,000,000 cases per year. Therefore, there exists a need fora therapeutic agent which will reduce the risk of development of skincancer or other consequences of skin photodamage even when applied afterexposure to sunlight has already occurred. Sunscreens and agents whichinduce or improve tanning are not useful in such situations, since theyare only useful if applied prior to exposure to UV radiation. Moreover,there are situations wherein sunscreens and even endogenous melanin canactually enhance UV-induced DNA damage through photodynamicsensitization.

[0005] There have been several attempts to improve or accelerate DNArepair and to reduce the consequences of DNA damage in skin cells afterdamage has already occurred. The first major step in DNA repair isdetection and excision of damaged portions of DNA. The viral enzyme T4endonuclease V can accomplish this step with some forms of DNA damage.T4 endonuclease V, when packaged in epidermis-penetrating liposomes, hasbeen shown to accelerate the rate of excision of pyrimidine dimers, themost common form of photolesion, in photodamaged skin of mice in vivo(Yarosh et al., Cancer Res. 52:4227-31, 1992). A bacterial extract hasbeen reported to increase the rate of unscheduled DNA synthesis, whichis often used as an index of DNA repair activity (Kludas and Heise, U.S.Pat. No. 4,464,362), in UV-exposed skin; however, this effect was notconfirmed in a subsequent study (Natarajan et al., Mutation Research206:47-54, 1988).

[0006] The key issue in DNA repair, however, is not necessarily the rateof lesion excision, but the fidelity of repair. Agents which acceleratethe excision step of DNA repair can actually exacerbate damage if thecells are incapable of accurate repair synthesis at a rate that matchesthe rate of excision of damaged segments of DNA (Collins and Johnson, J.Cell Physiol. 99:125-137, 1979).

[0007] Deoxyribonucleosides or deoxyribonucleotides have been added tocells in culture with variable or divergent effects on DNA damage ormutagenesis in response to irradiation of the cells. In some cell types,e.g. lymphocytes, which have limited capabilities for de novodeoxyribonucleotide synthesis, exogenous deoxynucleosides are reportedto improve cell survival after exposure to UV radiation (Yew andJohnson, Biochim. Biophys. Acta, 562:240-251, 1979; Green et al.,Mutation Research, 350:239-246, 1996) or ionizing radiation (Petrovic etal., Int. J. Radiat. Biol., 18:243, 1970); no significant improvement insurvival was seen after addition of deoxyribonucleosides toUV-irradiated normal human fibroblasts (Green et al., Mutation Research,350:239-246, 1996). A crucial point is that increasing cell survivalafter genomic damage caused by UV radiation or other mutagens is notnecessarily desirable. The process of programmed cell death, orapoptosis, is integrated with cellular mechanisms for detecting DNAdamage. Thus, genomic damage which by itself is not sufficient to causecell death, can trigger apoptosis, an active cellular suicide process,so that the DNA damage in the cell is not perpetuated in subsequent cellgenerations, with tumorigenesis as a possible outcome as genomic damageaccumulates. The mechanisms for detecting genomic damage and inducingapoptosis involve cell-cycle regulating proteins such as thetumor-suppressor protein p53. Therefore, agents which promote cellsurvival (e.g. by inhibiting apoptosis) after irradiation are notnecessarily anticarcinogenic, and may actually enhance mutationfrequency and risk of malignant transformation by permitting survival ofdamaged cells that would otherwise be eliminated by apoptosis. Asignificant illustration of this principle is the demonstration thatembryonic p53 knockout mice exposed to ionizing radiation in utero havea higher survival rate (live birth) than wild-type controls, but alsohave a much higher frequency of congenital defects (Norimura et al.,Nature Medicine, 2:577-580).

[0008] In studies where the effect of exogenous deoxyribonucleosides onmutation frequency in UV-irradiated cells has been explicitly studied,variable results have been obtained. Bianchi and Celotti (MutationResearch 146:277-284, 1985) reported that thymidine or deoxycytidine athigh concentrations increased the mutation frequency in UV-irradiatedV79 Chinese hamster cells; no reduction in mutation frequency wasobserved at any concentrations of added nucleosides. Musk et al.(Mutation Research 227:25-30, 1989) reported that a mixture ofdeoxyribonucleosides which included excess deoxycytidine relative to theother nucleosides, reduced the mutation frequency in response to UV-C(254 nm) irradiation in MM96L melanoma cells, a cell line with a knownconstitutive excess of purine deoxyribonucleotides. In the same study,exogenous deoxyribonucleosides had no effect on mutation frequency inanother neoplastic cell line, human HeLa cells, after exposure to UV-Cradiation. It is important to note that UV-C radiation is not acomponent of solar radiation at the surface of the earth, since it isblocked effectively by the atmosphere (Pathak, 1974, in Sunlight andMan, ed. by T. B. Fitzpatrick, University of Tokyo Press, Tokyo, Japan,p. 815). The effect of deoxyribonucleosides on mutation frequency incells exposed to solar radiation or UV radiation at wavelengths that arepresent in solar radiation was not tested, and the authors explicitlyconclude their discussion with the statement “ . . . the lower[mutation] frequency in sun-[irradiated] compared with UVC-irradiatedMM96L cells suggests that sunlight either does not perturb thedeoxynucleoside pools or it induces a cellular response that isinsensitive to nucleoside levels.” In addition to agents which inhibitapoptosis or improve DNA repair sufficiently to permit cell survival butnot necessarily for correction of potentially tumorigenic mutations,growth factors in general (including those that are involved in normalwound healing responses like TGF-β or PDGF) act as tumor promoters.

[0009] U.S. Pat. No. 5,246,708 discloses the methods and compositionsinvolving the use of mixtures of deoxyribonucleosides for promotion ofthe healing of wounds, ulcers, and burns, including those caused byultraviolet or solar radiation.

[0010] Acyl derivatives of deoxyribonucleosides have been taught asdelivery molecules for promoting entry of deoxyribonucleosides into theskin, as disclosed in U.S. patent application Ser. No. 466,379. It isdisclosed that acyl derivatives of deoxyribonucleosides can improvecellular repair and cell survival after damage to skin caused byradiation.

[0011] Oligodeoxyribonucleotides have been proposed as melanogenicstimuli, based on the idea that DNA damage, or excision products of DNAdamage, might be cellular signals for increasing melanin production inthe skin to help protect against subsequent damage. Gilchrest et al.(U.S. Pat. No. 5,470,577; WO Application Ser. No. 95/01773) proposedthat exogenous DNA photodamage products may stimulate melanogenesiswithout actual damage to cellular DNA as a necessary intermediate step.The stated intention was to mimic the presence of cyclobutane pyrimidinedimers or other DNA photodamage products in order to provide the cellwith false DNA damage signals that might trigger induction ofmelanogenesis in the absence of actual DNA damage. Treatment of melanomacells in vitro and guinea pig skin in vivo with thymidine dinucleotideresulted in increases in melanin production. The authors stated thatthey believed that DNA fragments entered the cells, and even theirnuclei, intact. They proposed that sunless tanning accomplished over aperiod of weeks by topical administration of oligodeoxyribonucleotides,especially thymidine dinucleotide, could protect skin by inducingmelanin synthesis, with consequent reduction of passage of UV radiationinto and through the skin.

[0012] Wiskemann (1974; in Sunlight and Man, ed. by T. B. Fizpatrick,University of Tokyo Press, Tokyo, Japan, p. 51) reported that systemic(intraperitoneal) administration the deoxyribonucleoside thymidine orthe ribonucleosides and congeners adenosine, cyclic-AMP, uridine,cytidine increased the period of latency for extravasation ofsystemically administered Evan's Blue dye in the skin in the first fewhours after UV exposure, indicating a reduction in acute UV-inducededema. In this system, DNA administered after irradiation had no effecton extravasation of dye. The author also explicitly states thatnucleobases incorporated into ointments do not penetrate the horny layer(the stratum corneum, the outer layer of enucleated keratinocytescomprising the main moisture barrier of skin) of human epidermis.

OBJECTS OF THE INVENTION

[0013] It is an object of the invention to provide compositions andmethods for reducing mutation frequency, photaging, and tumorigenesis inskin, thereby attenuating consequences of exposure to solar andultraviolet radiation and to other mutagens including endogenousoxidants.

[0014] It is an object of the invention to provide a composition thatenhances DNA repair and prevents consequences of mutagenic radiationeven when administered after damage or exposure to radiation or othermutagens has already occurred.

[0015] It is a primary object of this invention to provide compositionsand methods for effectively preventing or treating consequences ofexposure of the skin to solar and ultraviolet radiation and otherenvironmental mutagens.

[0016] It is a further object of the invention to provide compositionsand methods for improving the activity of chemical sunscreens.

[0017] It is a further object of the invention to provide compositionsand methods for reducing deleterious effects of sunscreens and othercompounds, exogenous and endogenous, which act as photosensitizing orphotodynamic enhancers of UV-induced damage to skin.

[0018] It is a further object of the invention to provide compositionsand methods for reducing some consequences of inflammatory skin andmucosal conditions, including psoriasis, dermatitis and inflammatorybowel disease.

SUMMARY OF THE INVENTION

[0019] The subject invention involves methods and compositions forimproving DNA repair (or genomic fidelity) and reducing photodamage inskin exposed to ultraviolet radiation, ionizing radiation, or chemicalmutagens by topical administration of compositions containing effectiveamounts of a source of deoxyribonucleosides. The compositions arecapable of delivering deoxyribonucleosides to the necessary targetcells. Such compositions are applied to the skin before, during or afterexposure to solar, ultraviolet, or ionizing radiation, or chemicalmutagens including but not limited to endogenous or exogenous sources offree radicals or nitric oxide. Treatment with compositions of theinvention improves the net fidelity of DNA repair and thereby reducesmutation frequency and the risk of tumorigenesis in response to solar orultraviolet radiation or other mutagens.

[0020] The invention provides methods and compositions for deliveringdeoxyribonucleosides to skin cells in concentrations sufficient tosupport and improve repair of damaged DNA and to reduce deleteriousconsequences of exposure of skin to radiation or chemical mutagens.

[0021] In addition to prevention of consequences of exposure tosunlight, compounds and compositions of the invention are useful fortreating skin lesions caused by sunlight like actinic keratoses or solarlentigenes.

[0022] The deoxyribonucleosides are administered either as freedeoxyribonucleosides, or as derivatives thereof which are converted todeoxyribonucleosides after application to the skin. Such derivativesinclude deoxyribonucleotides, oligonucleotides, DNA itself, and acylderivatives of deoxyribonucleosides or other derivatives ofdeoxyribonucleosides which are converted to free deoxyribonucleosides byendogenous enzymes.

[0023] Methods and compositions of the invention also improve activityand reduce side effects of other agents used on skin for prophylactic,therapeutic, or cosmetic purposes, including but not limited tosunscreens, retinoids, alpha-hydroxy acids, methylxanthines, and DNArepair enzymes.

[0024] The invention also relates to compositions and methods forreducing deleterious consequences (e.g. cellular damage, especially toDNA, which can result in increased likelihood of mutations or otherpotentially carcinogenic damage to the genome) of endogenous andexogenous photochemically-active compounds or chromophores which act asphotosensitizers or photodynamic enhancers of DNA damage caused by solaror ultraviolet radiation.

[0025] The invention, as well as other objects, features and advantagesthereof will be understood more clearly and fully from the followingdetailed description, when read with reference to the accompanyingresults of the experiments discussed in the examples below.

DETAILED DESCRIPTION OF THE INVENTION

[0026] DNA damage and repair is involved in the development of skincancer and photoaging. The subject invention provides compounds whichsuccessfully improve the net fidelity of DNA repair. The subjectinvention will have important consequences in health care and willimprove the cosmetic appearance of skin.

[0027] A. Definitions

[0028] The term “deoxyribonucleoside” refers to any one of the fourprinciple nucleoside constituents of DNA: deoxyadenosine, deoxycytidine,deoxyguanosine, and thymidine. The term “ribonucleoside” refers to anyone of the four major nucleoside constituents of RNA: adenosine,cytidine, guanosine, and uridine.

[0029] The term “acyl derivative of a deoxyribonucleoside” refers todeoxyribonucleosides bearing acyl substituents derived from carboxylicacids (which modify the pharmacokinetics and bioavailability of the freedeoxyribonucleosides), as disclosed in U.S. patent application Ser. No.466,379, hereby incorporated by reference in its entirety.

[0030] The term “source of at least one deoxyribonucleoside” or“deoxyribonucleoside source” in the context of the subject inventionrefers to deoxyribonucleosides themselves or derivatives ofdeoxyribonucleosides which can be converted to deoxyribonucleosides byendogenous enzymes, especially esterases. Examples include acylderivatives of deoxyribonucleosides (carboxylic acid esters),deoxyribonucleotides (phosphate esters), or oligodeoxyribonucleotides(phosphate diesters). Since esterase activity (involving various enzymescapable of cleaving carboxylic acid esters and phosphate esters) isubiquitous in mammalian tissues including skin, these esters ofdeoxyribonucleosides are converted to deoxyribonucleosides when appliedto skin. Similarly, a “source of at least one ribonucleoside” refers toa ribonucleoside or ribonucleoside ester, including a ribonucleotide, anoligoribonucleotide, or an acyl derivative of a ribonucleoside.

[0031] The term “ester of a deoxyribonucleoside” (or deoxyribonucleosideester) refers to either an acyl derivative of deoxyribonucleosides asdescribed above or to a phosphate ester of a deoxyribonucleoside (ordeoxyribonucleosides), e.g. deoxyribonucleotides,oligodeoxyribonucleotides, or polydeoxyribonucleotides.

[0032] The term “photosensitization” in the context of the subjectinvention refers to the process whereby light-absorbing (UV or visiblelight) molecules directly transfer the energy of an excited state,generally a triplet state, to a target molecule, resulting in damage toDNA and other cellular structures. The target molecule can be DNA itselfor another target which results in damage to DNA, e.g. membranescomponents of lysosomes, which contain deoxyribonuclease.

[0033] The term “photodynamic sensitization” herein refers to theprocess whereby UV-absorbing molecules generate free radical species orother diffusible reactive intermediates as a result of excitation by UVor visible radiation.

[0034] The term “sunscreen agents” refers to a UV-absorbing chemicalsthat are intended to be used in sunscreen products as active ingredientsfor reducing exposure of the skin to the UV component of solarradiation. Examples of sunscreen agents currently used as such incommercial products include avobenzone (t-butyldimethoxydibenzoylmethane), oxybenzone (benzophenone-3), dioxybenzone(benzophenone-8), sulisobenzone (benzophenone-4;2-hydroxy-4-methoxybenzophenone-5-sulfonic acid), octocrylene(2-ethylhexyl-2-cyano-3,3-diphenylacrylate), octyl methoxycinnamate(2-ethylhexyl p-methoxycinnamate), octyl salicylate(2-ethylhexylsalicylate), homosalate (homomenthyl salicylate), trolaminesalicylate (triethanolamine salicylate), phenylbenzimidazole sulfonicacid, PABA (para-aminobenzoic acid), roxadimate (ethyl 4-bishydroxypropyl aminobenzoate), lisadimate (glyceryl PABA), Padimate O(octyldimethyl PABA), menthyl anthranilate, and Parsol 1789 (butylmethoxydibenzoylmethane).

[0035] The term “energy scavenger” refers to a compound which absorbsenergy from the excited states of sunscreen agents or endogenousphotosensitizing or photodynamic enhancers of DNA damage, reducingdamage to target biological molecules like DNA. In this context, energyscavengers should be nontoxic at effective concentrations and shouldyield a net reduction in damage to DNA when present during UVirradiation in the presence of a photosensitizer or photodynamicenhancer of DNA damage. In the context of this invention, “energyscavengers” refer particularly to compounds with lowest triplet stateswith energies less than or equal to those of the nucleobase constituentsof genomic DNA. The primary quality of energy scavengers of theinvention is that, by virtue of photochemical energy state properties,or mass action (concentration), they prevent damage to genomic DNA thatwould otherwise occur due to energy transfer for excited chromophores,whether endogenous (e.g. melanin) or exogenous (e.g. sunscreens). Energyscavengers with photochemical properties similar to those of structuralconstituents of DNA are advantageous, and include sources of at leastone deoxyribonculeoside or ribonucleoside, like a deoxyribonucleoside,an acyl deoxyribonucleoside, a deoxyribonucleotide, anoligodeoxyribonucleotide, a ribonucleoside, a ribonucleotide, anoligoribonucleotide, and an acyl ribonucleoside.

[0036] The term “deleterious consequences” as used herein refers tocellular damage in a mammal caused by a mutagen, especially damage tothe genome, resulting in an increased chance of developing skin canceror other skin lesions like solar lentigines, actinic keratoses, or othersigns of photoaging like skin wrinkles or “age spots”. Mutagens capableof causing such deleterious consequences include solar radiation,ultraviolet radiation, ionizing radiation, free radicals (whetherproduced as a result of irradiation of a photochemically activechromophore or from some other source, including normal metabolicprocesses), nitric oxide, and environmental mutagens.

[0037] B. Compounds of the Invention

[0038] The compounds of the invention are primarily the majordeoxyribonucleoside constituents of DNA: deoxyadenosine, deoxycytidine,deoxyguanosine, and thymidine. The invention also includes the use ofeffective amounts of precursors of these deoxyribonucleosides, e.g.oligodeoxyribonucleotides, DNA, deoxyribonucleotides and acylderivatives of deoxyribonucleosides, and, particularly for minimizationof effects of photodynamic sensitizers and photosensitizing agents onDNA, ribonucleosides and their congeners, e.g. oligoribonucleotides,ribonucleotides, and acyl derivatives of ribonucleosides.

[0039] 2-Deoxyribose and acyl derivatives of 2-deoxyribose are alsouseful compounds of the invention. They are particularly advantageousfor use in treatment of existing sunlight-induced skin lesions likeactinic keratoses.

[0040] While not wishing to be bound by a theory, it is believed thatthe active agents of the invention that pass into cells are thedeoxyribonucleosides or acyl derivatives of deoxyribonucleosides, sincethe anionic phosphate moiety on deoxyribonucleotides oroligodeoxyribonucleotides impedes passage across cell membranes.Phosphorylated deoxyribonucleoside precursors are converted to freedeoxyribonucleosides by enzymatic and nonenzymatic degradation before orafter application to the skin, prior to their entry into cells.

[0041] The deoxyribonucleosides are produced by any of several methods.They are produced by degradation of DNA from biological sources, e.g.fish sperm, by chemical synthesis, or by fermentation technology.

[0042] Also encompassed by the invention are pharmaceutically acceptablesalts of the above-noted compounds.

[0043] C. Compositions of the Invention

[0044] The invention includes pharmaceutical compositions for improvingthe net fidelity of DNA repair and for protecting the skin againstmutagens. The composition comprises 1) an effective amount of a sourceof one or more deoxyribonucleosides, and optionally 2) an effectiveamount of a pharmaceutically acceptable topical carrier capable ofdelivering the deoxyribonucleosides or their precursors to appropriatetarget cells in the skin under in vivo conditions.

[0045] While individual deoxyribonucleosides, especially deoxycytidine(see Example 7) have some activity in attenuating UV-inducedtumorigenesis, two or more deoxyribonucleosides, or preferably all four,are typically included in a formulation of the invention. Encompassed bythe invention are compositions containing deoxyadenosine, deoxycytidine,deoxyguanosine, or thymidine, either as single agents, or in allpossible combinations of two, three, or all four of these compounds.Compositions containing deoxycytidine are particularly advantageous. Theconcentrations of individual deoxyribonucleosides in compositionsencompassed by the invention, whether present individually or incombination with other deoxyribonucleosides or deoxyribonucleosideprecursors (such as deoxyribonucleoside esters), and normalized to theamount of free nucleoside or nucleoside moiety in the case ofdeoxyribonucleoside phosphates or oligonucleotides or prodrugs likeacylated deoxyribonucleoside derivatives, range from 0.1 to 10 mg/ml,advantageously 1 to 5 mg/ml.

[0046] In the case of deoxyribose or acyl derivatives of deoxyribose,appropriate concentrations in a composition of the invention range from0.1 to 100 millimolar, advantageously 10 to 50 millimolar.

[0047] In order to permit access of the deoxyribonucleosides and relatedcompounds of the invention to deeper-lying skin cells, vehicles whichimprove their penetration through the outer layers of the skin, e.g. thestratum corneum, are useful. Vehicle constituents which improve thepenetration of compounds of the invention into the skin include but arenot limited to: ethanol, isopropanol, diethylene glycol ethers such asdiethylene glycol monoethyl ether, azone(1-dodecylazacycloheptan-2-one), oleic acid, linoleic acid, propyleneglycol, hypertonic concentrations of glycerol, lactic acid, glycolicacid, citric acid, and malic acid.

[0048] Appropriate concentrations of diethylene glycol monoehtyl etherin compositions of the invention range from 2 to 20 percent,advantageously from 5 to 15 percent, on a weight/weight basis.

[0049] In addition to promoting absorption of agents into the skin, useof topical alpha-hydroxy acids (AHA), e.g. lactic acid and glycolicacid, can affect the ability of the skin to reduce the penetration ofultraviolet light into the vulnerable basal layers of the epidermis.Thus, there is also an increased need for agents which reduce theconsequences of exposure to solar or ultraviolet radiation in peopleusing AHA's, e.g. for promoting exfoliation of epidermal cells. Sincepenetration of UV-absorbing sunscreen agents into the skin isundesirable because of possible photosensitization and photodynamicenhancement of UV-induced damage to cells, the compounds of theinvention are uniquely suitable for combination with AHA's, either inthe same formulation or a separate one, for improving skin resistance todamaging effects of solar or ultraviolet radiation.

[0050] One embodiment of the invention is a hydrogel formulation,comprising an aqueous or aqueous-alcoholic medium and a gelling agent,and a deoxyribonucleoside source. Suitable gelling agents include butare not limited to methylcellulose, carboxymethylcellulose,hydroxypropylmethylcellulose, carbomer (carbopol), hypan, polyacrylate,and glycerol polyacrylate.

[0051] Concentrations of gelling agents are selected according to theireffect on viscosity and pharmaceutical and cosmetic propoerties.Suitable concentrations of a carbomer gelling agent, e.g. carbomer 934P,range from 1 to 15%, advantageously 2 to 10% on a weight/weight basis.

[0052] Liposomes are microscopic lipid vesicles which can containpharmacologically active agents either enclosed in the aqueous spacewithin the vesicle or in the lipid membrane itself, depending on thelipophilicity of the agent. Liposomes are capable of delivering apharmacologic agent through the stratum comeum into deeper layers of theskin, and are therefore suitable vehicles for compounds and compositionsof the invention.

[0053] Niosomes are lipid vesicles similar to liposomes with membranesconsisting largely of non-ionic lipids, some forms of which areeffective for transporting compounds across the stratum corneum.

[0054] In one embodiment of the invention, lipophilic acyl derivativesof deoxyribonucleosides, e.g. oleic or palmitic acid esters ofdeoxyribonucleosides are incorporated into membranes of niosome orliposome membranes, in addition to or instead of being enclosed withinthe vesicular membranes.

[0055] Other agents which are advantageous for incorporation into acomposition of the invention include corticosteroids, especiallyhydrocortisone in concentrations of 0.05 to 1%, other anti-inflammatorycorticosteroids at therapeutically effective concentrations, topicalanesthetics including but not limited to benzocaine, lidocaine, andbenzyl alcohol, aloe vera and aloe barbadensis, retinoids, antioxidantslike Vitamins C and E, flavins, polyphenols (e.g. extracted from greentea or black tea), allantoin, liposomal DNA repair enzymes,antibacterial agents (e.g. quaternary ammonium compounds, bacitracin,neomycin, polymyxin), zinc salts, and methylxanthines. All of theselisted agents have some utility in treating or attenuating variousaspects of skin injury or discomfort caused by ultraviolet radiation orinflammatory skin conditions, and are therefore complementary to theunique actions of the deoxyribonucleosides of the invention.

[0056] Benzyl alcohol, which is known to have anesthetic andpreservative properties, has the unexpected effect of improving aqueoussolubility of the relatively insoluble purine deoxyribonucleosides,deoxyadenosine and deoxyguanosine; preferred concentrations of benzylalcohol in topical formulations of deoxyribonucleosides are 0.5 to 5%.This is very important in permitting high concentrations of thedeoxyribonucleosides of the invention to be stably incorporated intoaqueous vehicles.

[0057] Sunscreens

[0058] The compounds of the invention are advantageously incorporatedinto the same formulation as a UV-absorbing chemical sunscreen agentsuch as: avobenzone (t-butyl dimethoxydibenzoylmethane), oxybenzone(benzophenone-3), dioxybenzone (benzophenone-8), sulisobenzone(benzophenone-4; 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid),octocrylene (2-ethylhexyl-2-cyano-3,3-diphenylacrylate), octylmethoxycinnamate (2-ethylhexyl p-methoxycinnamate), octylsalicylate(2-ethylhexylsalicylate), homosalate (homomenthyl salicylate),trolamine salicylate (triethanolamine salicylate), phenylbenzimidazolesulfonic acid, PABA (para-aminobenzoic acid), roxadimate (ethyl 4-bishydroxypropyl aminobenzoate), lisadimate (glyceryl PABA), Padimate O(octyldimethyl PABA), menthyl anthranilate, or Parsol 1789 (butylmethoxydibenzoylmethane).

[0059] Alternatively, the compounds of the invention are formulated in abase which is suitable for application to the skin prior to, or after,application of a sunscreen. This embodiment of the invention permits thebenefits of deoxyribonucleosides, in reducing consequences of UV damageand in attenuating photodynamic enhancement of cellular damage caused bysunscreen agents themselves, to be obtained in conjunction with use of awide variety of commercial sunscreen products.

[0060] D. Therapeutic Uses of the Compounds and Compositions of theInvention

[0061] Reduction of Deleterious Consequences of Exposure of Skin toUltraviolet or Solar Radiation

[0062] The compounds and composition of the invention, when applied oradministered before, during, or after exposure of the skin of a mammalto mutagenic radiation, have the unexpected activity of improving thenet fidelity DNA repair, thereby reducing mutation frequency,photoaging, and the chance of developing skin cancers.

[0063] DNA repair proceeds by several steps. A chemical lesion in DNA,which can be caused by ultraviolet radiation, ionizing radiation, freeradicals, or chemical mutagens, is detected by the DNA repair system. Asegment of nucleotides including the damaged region is excised,generally along with a number of surrounding nucleotides. The excisedstrand is then resynthesized from free deoxyribonucleotides, using theintact DNA strand as a template.

[0064] It is generally believed that improvement of repair of DNA inskin cells (e.g. keratinocytes, melanocytes, fibroblasts) would requirealteration in the activity of enzymes or other proteins involved in thedetection and excision of DNA lesions. Thus, there have been attempts toimprove DNA repair in skin by delivering DNA repair enzymes viatopically-applied liposomes (U.S. Pat. No. (Yarosh et al., Cancer Res.52:4227-31, 1992).

[0065] Far more important than the initial rate of excision of lesionsis the fidelity or accuracy of repair. Agents which accelerate theexcision step of DNA repair can actually exacerbate damage if the cellsare incapable of accurate repair synthesis at a rate that matches therate of excision of damaged segments of DNA (Collins and Johnson, J.Cell Physiol. 99:125-137, 1979).

[0066] Compounds and compositions of the invention, when applied to skinbefore, during or after exposure to solar or ultraviolet radiation orother environmental mutagens, reduces the mutation frequency otherwiseinduced by the mutagen (Example 1). This reduces the damage to cellscaused by the mutagen, and reduces the chance of development of skincancers, as shown in Examples 2 and 7. The effect on genomic fidelity isin principle mediated by actual improvement in the fidelity of repair inan individual cell or by improvement of the elimination of cells withirreparable DNA damage. Either mechanism results in a net improvement ingenomic fidelity in skin exposed to mutagens.

[0067] The compounds of the invention have unanticipated benefits whenused in combination with other agents known to be useful in variousaspects of skin care, including but not limited to sunscreens,methylxanthines, retinoids, DNA repair enzymes, exfoliants, and proteaseinhibitors, corticosteroids and nonsteroidal anti-inflammatory agents.

[0068] The compounds and compositions of the invention, when appliedsoon enough, e.g. within about 3 days after exposure to ultraviolet orsolar radiation, improve the repair of cellular and macromoleculardamage and improve net genomic fidelity, thereby reducing the chance ofdevelopment and severity of macroscopically visible deleteriousconsequences of such exposure, including but not limited to photoaging,sunburn symptoms, actinic keratoses, solar lentigines, “age spots”, andskin cancer, e.g. basal cell carcinoma, squamous cell carcinoma,melanoma. The compounds and compositions of the invention are alsooptionally applied before or during exposure to solar or ultravioletradiation to shorten the time gap between damage and onset of repairenhancement by the compounds of the invention.

[0069] Treatment of skin with compounds and compositions of theinvention results in a reduced chance of development of skin cancers andother deleterious consequences of exposure to solar or UV radiation likephotaging even when the compounds of the invention are applied evenafter irradiation, e.g. after unintended exposure topotentially-damaging doses of solar radiation. This type of activity isnot shared by conventional sunscreens or agents which might act byenhancing melanogenesis, which are useful only if applied beforeirradiation.

[0070] Compounds and compositions of the invention are furthermoreuseful for treating existing inflammatory or hyperproliferative skinlesions, especially those caused by exposure to sunlight or ultravioletradiation, including but not limited to actinic keratoses, solarlentigines, and wrinkles. Example 9 illustrates this activity in apatient, in which topical application of a composition of the inventionresulted in complete regression of an an existing actinic keratosis.

[0071] Improvement of Sunscreen Activity and Attenuation of PhotodynamicEnhancement of UV Damage by Sunscreens

[0072] Sunscreens are typically designed and tested on the basis ofprevention of sunlight-induced erythema. While erythema and itsattenuation by sunscreens is an important short-term effect, reductionof erythema and inflammation by sunscreens does not necessarily meanthat they produce a proportionate protection of DNA (or prevention ofskin cancers and some features of photoaging secondary to DNA damage).Sunscreens are certainly useful in preventing some manifestations ofphotoaging and UV-related carcinogenesis, but do not provide completeprotection, and in some situations may actually exacerbate photoinjuryby acting as photodynamic sensitizers (see Example 3).

[0073] Chemical sunscreens are intended to act by absorbing photons atmutagenic (or erythmogenic) wavelengths, thus producing a short-livedexcited singlet state; return to the ground state is accompanied byphoton emission at longer wavelengths that are supposed to be lessharmful than the incident radiation. Photon emission during the rapidreturn of a molecule from an excited singlet state to a ground state isknown as “fluorescence”. However, sunscreens or other exogenous orendogenous UV-absorbing molecules can also be excited to longer-livedtriplet states which can facilitate further reactions (theenergy-emission that occurs during return of a molecule from an excitedtriplet state to a ground state is known as “phosphorescence”, andtypically occurs over a much longer time span than fluorescence). Theconsequence is that some UV-absorbing agents, especially those with alowest triplet state that has a higher energy level than the lowesttriplet state of genomic DNA constituents, can absorb photons andactually exacerbate damage to DNA by direct or indirect energy transfer(e.g. from a triplet excited state) rather than by simple fluorescence,or photon emission at harmless wavelengths.

[0074] Benzophenone, a close structural analog of oxybenzone, increasesthe yield of strand breaks and pyrimidine dimers in UV-irradiated DNA,and is known to produce free radicals upon irradiation with UV light(Charlier et al., Photochemistry and Photobiology, 15:527-536, 1972).The results presented in Examples 3, 4, 5 and 6 indicate that a similarphenomenon also occurs with approved sunscreen ingredients, and that thedeoxyribonucleosides of the invention attenuate this deleteriousconsequence of sunscreen use.

[0075] When present in concentrations sufficient to block access of UVradiation to cells, sunscreen agents are protective. However, if presentin very low concentrations, insufficient to adequately block UVtransmission, photon-absorbing agents, including common sunscreeningredients, can operate as energy-transfer molecules, efficientlytrapping UV energy and transferring it to cell components, eitherdirectly (photosensitization) or by catalyzing formation of reactiveoxygen radicals (photodynamic sensitization). Thus, low concentrationsof oxybenzone, for example, enhance DNA damage induced by ultravioletradiation, whereas higher concentrations, sufficient to block UV accessto the cells or their immediate microenvironment altogether, protectagainst DNA damage (see Example 3).

[0076] The expected activity in vivo is that an oxybenzone-containingsunscreen would protect cells from damage if present in a layersufficient to block access of light to the target cells altogether.However, at lower concentrations, insufficient to prevent penetration ofUV radiation to target cells, and especially if some oxybenzone has beenabsorbed into the critical cell layers, either via passage through thestratum corneum or through hair follicles, there may be potentiation ofdamage to DNA in vivo. In mice treated topically with commercialsunscreen containing oxybenzone, effects consistent with this hypothesisare in fact observed after exposure to UV (see Example 6). Classes ofsunscreens other than benzophenone derivatives also exacerbateUV-induced damage to DNA when present at low concentrations duringirradiation.

[0077] A strain of transgenic mice (v-HA-ras transgenic TG.AC mice)which is very susceptible to a variety of carcinogens, including UVradiation has been developed recently (Leder et al., Proc. Nat. Acad.Sci. USA, 87:9178-9182, 1990). In response to a relatively smallexposure to UV radiation, these mice reliably develop cutaneouspapillomas within a few weeks. When a circular patch of commercialsunscreen is applied to the back of such a mouse, the center of theprotected region does in fact have lower incidence of UV-inducedpapillomas than the unprotected side, but often, along the margin of theapplied sunscreen, there is a very high incidence (sometimes higher thanin unprotected areas) of papillomas (See Example 6). A layer ofsunscreen sufficient to block UV access to target cells is protective,but low concentrations, e.g. at the margin of a patch of sunscreen) canact as photosensitizers increasing the incidence of a UV-induced skincancer beyond that seen in completely “unprotected” skin. Exposure ofrelevant skin cells to low photosensitizing (rather than protective)concentrations of sunscreens clearly must occur during ordinary usage,e.g. at the margin of an applied patch, or as a protective layer iswashed or worn off.

[0078] A benefit of deoxyribonucleosides or related compounds added toconventional sunscreen formulations (or other cosmetics containingsunscreens), beyond the support of DNA repair, is to synergize withconventional sunscreen compounds by acting as energy scavengers whichtrap energy emitted by (or radicals produced by) sunscreen agents thatis chemically similar to the cellular target, DNA. Exogenousdeoxyribonucleosides (in addition to their direct absorbance of UVenergy) serve as “decoys” for energy captured by sunscreen agents orother photosensitizers that would otherwise be transferred to cellulartargets, including DNA. Thus, deoxyribonucleosides provide adose-dependent reduction in damage caused to cellular DNA by UVradiation in the presence of low concentrations of photosensitizingagents like oxybenzone or other sunscreen agents (Example 4).

[0079] A defining characteristic of suitable energy scavenging agents isthat their lowest triplet energy state is equal to or lower than that ofDNA constituents in situ. Because of the similarity of physicochemicalproperties of deoxyribonucleosides (or deoxyribonucleotides, acyldeoxyribonucleosides, or oligodeoxyribonucleotides) and genomic DNA, thecompounds of the invention are particularly suitable asenergy-scavenging agents to protect genomic DNA from damage due toenergy transfer from photosensitizers or photodynamic sensitizers. Inthis embodiment, ribonucleosides, ribonucleotides, oligoribonucleotidesand acyl derivatives of ribonucleosides are within the scope of theinvention. Appropriate concentrations of such scavengers in acomposition for topical application range from 0.1 to 100 milligrams permilliliter (normalized to the amount of free nucleoside present in thecase of nucleotides or oligonucleotides or acyl derivatives ofnucleosides). Advantageously, such scavengers are present inconcentrations ranging from 0.1 to 20 mg/ml or especially 1 to 5 mg/ml.

[0080] The problem of photodynamic enhancement of damage to DNA extendsbeyond sunscreens. Other compounds including endogenous molecules in theskin, can absorb UV radiation at wavelengths that do not necessarilydirectly damage DNA significantly, and transfer that energy to cellulartargets including DNA, or generate free radicals that damage cellularDNA. Examples of endogenous photosensitizing or photodynamically activeskin constituents (photochemically active chromophores) include but arenot limited to porphyrins, tryptophan, riboflavin, and melanin.Exogenous photodynamically active compounds include psoralens, which arepresent in some perfume oils (bergamot), and which are in fact used toenhance sunlight-induced tanning and UV phototherapy of psoriasisthrough exacerbation of cellular injury. Many therapeutic drugs or theirmetabolites are photochemically active chromophores which can produceskin adverse reactions when a patient is exposed to solar, visible, orultraviolet radiation. Pigments and other light-absorbing constituentsof cosmetics are also photochemically active chromophores which canexacerbate cellular photodamage.

[0081] The deoxribonucleosides and related compounds of the invention(e.g. deoxyribonucleotides, oligonucleotides, or DNA itself) are usefulfor attenuating cellular damage caused by excited light-absorbingmolecules, including exogenous photochemically active chromophores likesunscreens and cosmetic pigments, and also from endogenous chromophoreslike tryptophan, porphyrins, urocanic acid and melanin.

[0082] Furthermore, since the photodynamic enhancement of DNA damagecaused by benzophenone derivatives is in part mediated by production offree radicals (Charlier et al., Photochemistry and Photobiology,15:527-536, 1972), compounds and compositions of the invention areuseful for protecting the skin and mucosa from free radical damage,whether or not the free radicals (e.g. hydroxyl radicals, peroxideradicals, or lipoperoxide radicals) are initiated or produced byphotodynamic phenomena. Examples 3,4,5 and 6 provide evidence that thedeoxyribonucleosides of the invention protect against DNA caused by freeradicals.

[0083] The deoxyribonucleosides and related compounds of the inventionare advantageously incorporated into the same formulation as chemicalsunscreen agents, which include but are not limited to: avobenzone(t-butyl dimethoxydibenzoylmethane), oxybenzone (benzophenone-3),dioxybenzone (benzophenone-8), sulisobenzone (benzophenone-4),octocrylene (2-ethylhexyl-2-cyano-3,3-diphenylacrylate), octylmethoxycinnamate (2-ethylhexyl p-methoxycinnamate), octyl salicylate(2-ethylhexylsalicylate), homosalate (homomenthyl salicylate), trolaminesalicylate (triethanolamine salicylate), phenylbenzimidazole sulfonicacid, PABA (para-aminobenzoic acid), roxadimate (ethyl 4-bishydroxypropyl aminobenzoate), lisadimate (glyceryl PABA), Padimate O(octyldimethyl PABA), menthyl anthranilate, or Parsol 1789 (butylmethoxydibenzoylmethane). Such sunscreen agents are present informulations at concentrations that are in accord with regulatoryguidelines and standard use.

[0084] Similarly, in another embodiment of the invention, compounds ofthe invention are incorporated into cosmetics containing photochemicallyactive chromophores to minimize deleterious consequences of combinedexposure of skin to solar or ultraviolet radiation and such cosmeticingredients.

[0085] Alternatively, the compounds of the invention are applied to theskin in a separate composition, e.g. a spray, lotion, roll-on, stick, orgel, before or after a sunscreen product or cosmetic is applied.

[0086] Methylxanthines

[0087] Methylxanthines, such as caffeine, theophylline, aminophylline orisobutylmethylxanthine, have been proposed as “sunless” tanning agents,which act by modulating activity of the biochemical pathways involved inmelanogenesis. Their proposed mechanism involves inhibition ofcyclic-AMP phosphodiesterase, thus enhancing the biological activity ofcyclic AMP in the pathways regulating melanogenesis. Methylxanthines canenhance the production of melanin in melanocytes, acting either alone orin combination with tanning stimulants like ultraviolet or solarradiation. However, methylxanthines are also known to exacerbate DNAdamage caused by ultraviolet radiation, which has been attributed to animpairment of DNA repair or disruption of cell cycle control mechanisms(Kastan et al., Cancer Research, 51:6304-6311, 1991).

[0088] Compounds of the invention are useful for reducing thedeleterious effect of methylxanthines on DNA damage caused by exposureof skin to ultraviolet or solar radiation. The compounds of theinvention thus improve the safety of skin tanning products that containmethylxanthines as active ingredients. Compounds of the invention areapplied either separately or in the same formulation as themethylxanthines.

[0089] Exfoliants

[0090] Cosmetics containing alpha-hydroxy acids (AHA) such as lacticacid, glycolic acid, citric acid, or malic acid are widely used. Theyhave moisturizing and exfoliant properties. Products containing highconcentrations of AHA are also used to produce more extreme “skinpeels”, in which the outer layers of the epidermis are removed,essentially by means of a chemical burn. New epidermis growing in isoften softer and smoother than the skin layers that were removed.Beta-hydroxy acids like salicylic acid are also useful exfoliants.Retinoic acid is used for similar purposes through its exfoliant actionsand through stimulation of epidermal cell turnover and alteration ofepidermal metabolism.

[0091] Exfoliants are reported to reduce the sun-blocking capabilitiesof the stratum corneum, and furthermore increase the permeability of theskin to other agents. Thus, there is a need for use of UV protection inconjunction with AHA's, yet the increased skin permeability produced byAHA requires caution in the selection of sun protection agents, sinceabsorbed sunscreen agents can produce photodynamic enhancement of DNAdamage. The compounds of the invention are effective in reducingdeleterious consequences of exposure to sunlight or ultravioletradiation or other environmental mutagens in subjects using exfoliants,including but not limited to alpha-hydroxy acids, beta-hydroxy acids,and retinoids.

[0092] Nonsteroidal Anti-inflammatory Agents

[0093] Nonsteroidal anti-inflammatory agents are commonly used fortreatment of arthritis and other anti-inflammatory agents. Moreover,some members of this class, e.g. diclofenac(2,6-dichloro-phenyl-amino-phenylacetate) are under investigation astopical agents for reducing some aspects of skin photodamage.

[0094] One of the prototypical members of this class of drugs,acetaminophen, inhibits DNA repair after damage caused by UV radiationby inhibiting the enzyme ribonucleotide reductase, which convertsribonucleoside diphosphates to deoxyribonucleoside diphosphates (Hongsloet al., Mutagenesis, 8:423-429, 1993). By supplying deoxyribonucleosidesto skin, especially to areas of the skin that are generally exposed tosunlight, of patients receiving either oral or topical treatment withnonsteroidal anti-inflammatory agents, compositions of the inventionovercome a deleterious consequence associated with this widely-usedclass of drugs.

[0095] Ornithine Decarboxylase Inhibitors

[0096] One consequence of UV irradiation of skin is an increase in cellproliferation rate and in the activity of enzymes necessary for cellproliferation, one of which is ornithine decarboxylase (ODC).Difluoromethylornithine (DFMO) is an inhibitor of ODC, which isnecessary for polyamine synthesis, which in turn is necessary for DNAreplication. DFMO is useful for reducing the incidence of skin cancerand precancerous actinic lesions. Inhibition of cell cycling afterexposure to solar or UV radiation may give cells more time to repair DNAbefore mutagenic lesions are fixed by cell division, but cell cyclestasis also generally results in reduced levels of deoxyribonucleosides,which are necessary for repair of DNA damage. Deoxyribonucleosides aretherefore useful in conjunction with DFMO and other antiproliferativeagents which act via mechanisms not directly involving induced depletionor imbalance of deoxyribonucleotide pools. Deoxyribonucleosides of theinvention are optionally incorporated into the same formulation as DFMO(or other inhibitors of skin cell proliferation that act throughmechanisms other than impairment of DNA precursor synthesis), or areapplied in a separate formulation.

[0097] Treatment of Skin During Exposure to Endogenous Nitric Oxide

[0098] Nitric oxide (NO) is a biologically active mediator released byendothelial cells, macrophages and other cell types, especially duringinflammatory episodes. Nitric oxide is also an important mediator oferythema associated with UV exposure. Inhibitors of NO synthetaseattenuate the increase in skin blood flow following exposure(Deliconstantinos et al., J Cardiovasc Pharmacol 20 Suppl 12:S63-5,1992; Deliconstantinos et al., Br J Pharmacol 114(6):1257-65, 1995;Warren, FASEB Journal, 8(2):247-51, 1995).

[0099] Nitric oxide is a potent inhibitor of the enzyme ribonucleotidereductase (RR), which is the key enzyme for de novo synthesis ofdeoxyribonucleotides (Kwon et al., J Exp Med 174(4):761-7, 1991;Lepoivre et al., J Biol Chem 269(34):21891-7, 1994) Theantiproliferative effects of nitric oxide are in part attributable toinhibition of ribonucleotide reductase. This can be beneficial in aninflammatory response to an infectious microorganism or a neoplasm, butis deleterious in cells in need of capability for DNA repair, e.g. skinexposed to inflammatory mediators elicited by UV exposure. The amountsof NO released from macrophages are sufficient to inhibit ribonucleotidereductase and thereby induce cytostasis in neighboring cells.

[0100] The best-known inhibitor of RR, hydroxyurea (HU), has structuralsimilarities to N-omega-hydroxy-1-arginine, a physiological intermediatein NO production. Hydroxyurea can act as an NO-like nitrosating reactant(LePoivre et al., J Biol Chem 269(34):21891-7, 1994). Both NO andhydroxyurea inhibit RR by quenching a tyrosyl radical in the active siteof the enzyme.

[0101] A discovery first disclosed herein is that NO sensitizes cells toUV-induced DNA damage via mechanisms that are reversible with exogenousdeoxyribonucleosides (see Example 8). Moreover, NO by itself, in theabsence of UV exposure, causes DNA damage that is prevented or reversedby compounds of the invention (Example 8).

[0102] The inflammatory response to UV exposure (which also plays animportant role in UV-associated immunosuppression), via inhibition ofribonucleotide reductase by NO, exacerbates the mutagenic and cytotoxiceffects of UV exposure. The subject invention provides a means forcompensating for this deleterious effect of NO. Exogenousdeoxyribonucleosides, which enter into DNA metabolism downstream ofribonucleotide reductase, compensate for reduced RR activity. NO,although deleterious in cells needing deoxyribonucleotides, has somebeneficial effects in sun-exposed skin. Inhibitors of NO production alsoimpair the healing of skin damaged by exposure to excessive UVradiation, i.e., UV doses that produce a sufficiently severe sunburn forwound healing processes to be called into action (Benrath et al.,Neurosci Lett, 1995). Thus, NO is useful for tissue repair (probably byimproving blood flow and perhaps also by stimulating growth factorrelease from macrophages or keratinocytes), but may simultaneouslyexacerbate UV-related damage to DNA by reducing cellular capacities forproduction of deoxyribonucleotides for DNA repair.

[0103] NO-mediated inhibition of RR provides a mechanism for adisproportionate increase in DNA damage without a corresponding increasein other symptoms of sun exposure during repeated exposure to strongsunlight. Topical application of the compounds and compositions of theinvention provides a method for ameliorating this form of conditionalhypersensitivity.

[0104] NO participates in skin inflammatory reactions that do notnecessarily involve exposure to solar or ultraviolet radiation. NO,which is released from activated macrophages, is component of mostinflammatory reactions. The compounds and methods of the inventionprovide a means of overcoming some deleterious effects of NO ininflammatory skin conditions, including but not limited to psoriasis,dermatitis, allergic dermatitis, contact dermatitis (e.g. reactions topoison ivy and poison oak), eczema and acne. In these conditions, NOsensitizes some cell types to UV-induced DNA damage by inhibitingdeoxyribonucleotide synthesis. Compounds and compositions of theinvention ameliorate this deleterious consequence of combined UVexposure and inflammatory skin conditions. Since NO and other endogenousoxidants that cause DNA damage are present in inflammatory skinconditions like psoriasis or dermatitis even in the absence ofsignificant exposure to UV radiation, the deoxyribonucleosides of theinvention are useful for protecting genetic integrity of skin cells ininflammatory conditions. Compounds of the invention prevent or repairDNA damage caused by NO alone, without exposure to UV radiation (Example8).

[0105] Ribonucleosides are also useful for treating inflammatory skin anmucosal conditions, in part by providing higher concentrations of theribonucleotide substrates for ribonucleoside reductase. Ribonucleosides(or ribonucleoside esters) in this context are used in the same waysthat deoxyribonucleosides, advantageously in topically-appliedcompositions, with ribonucleosides (or ribonucleoside esters)incorporated in concentrations ranging from 0.1 to 20 mg/ml,advantageously 1 to 5 mg/ml. Adenosine is particularly useful fortreatment of inflammatory conditions.

[0106] Inhibition of DNA precursor synthesis by hydroxyurea leads toenhanced activity and leakage of hydrolytic lysosomal enzymes whichparticipate in extracellular damage, e.g. in inflammatory skinconditions or photodamage (Malec et al., Chem. Biol. Interact.,57:315-324, 1986). The compounds of the invention prevent this componentof inflammatory tissue injury, especially when such inhibition of DNAprecursor synthesis is mediated by endogenously-produced NO, which isfunctionally similar to hydroxyurea.

[0107] A further contribution to genomic damage is that exposure ofcells to ultraviolet radiation results in the release of enzymes,including deoxyribonuclease, from lysosomes. Deoxyribonuclease II, whichis present in lysosomes, is an endonuclease that can produce strandbreaks in nuclear DNA following lysosome disruption. Leakage of enzymesfrom lysosomes also occurs in inflammatory conditions in general. Thecompounds and compositions of the invention are useful for preservinggenomic integrity after chromosomal damage caused by deoxyribonucleasereleased from lysosomes in inflammatory skin conditions and afterexposure of skin to solar or ultraviolet radiation.

[0108] By limiting some of the deleterious consequences of skininflammation, compounds and compositions of the invention are useful asanti-inflammatory agents, and are optionally administered (either asseparate compositions or, advantageously, in the same formulation) inconjunction with other topical or systemic anti-inflammatory agentsincluding but not limited to corticosteroids like hydrocortisone and itscongeners.

[0109] Similarly, compounds and compositions encompassed by theinvention are useful for treatment of mucosal inflammatory conditions,including but not limited to inflammatory bowel disease, ulcerativecolitis, or Crohn's disease, or mucositis anywhere in thegastrointestinal tract. The preferred mode of treatment is by topicaladministration, in this case via enema or suppository, for whichpurposes deoxyribonucleosides or other compounds of the invention areincorporated into suitable vehicles.

[0110] Treatment of Skin and Mucosal Tissues Exposed to IonizingRadiation

[0111] Patients receiving therapeutic treatment (e.g. for cancer) withionizing (X-Ray or gamma) radiation can suffer damage to skin overlyingan internal tumor, leading to desquamation and poor healing. Compoundsand compositions of the invention are useful for treating damage to skinand mucosal surfaces caused by intentional or accidental exposure toionizing radiation. For treatment of skin, compositions of the inventionare applied topically before or after radiation treatment. For treatmentof mucosal surfaces, e.g. in the mouth, gastrointestinal tract, urethraor vagina, appropriate compositions of the invention are also appliedtopically. Suitable compositions for treatment of mucosal surfacesinclude gels, lotions, ointments, suppositories, orally-administeredcapsules, pills or dragees, or solutions.

[0112] E. Administration and Formulation of Compounds and Compositionsof the Invention

[0113] Compounds of the invention are formulated in pharmaceuticallyacceptable vehicles that deliver the compounds to the necessary cellpopulations in skin at concentrations adequate to accomplish theobjectives of reducing mutation frequency and chance of developingcancer.

[0114] Compositions of the invention are applied before, during, orafter exposure to sunlight or other mutagens. A lotion or hydrogelcontaining deoxyribonucleosides (0.1 to 10 mg/ml, advantageously 1 to 5mg/ml) is applied to skin as a thin film. The composition should beapplied within about 48 or 72 hours after exposure to damaging doses ofsunlight or ultraviolet radiation, in order to provide support for DNArepair prior to the first cell divisions after irradiation, althoughapplication before, during, or within 12 hours after exposure to intensesunlight is advantageous. Compositions of the invention are alsoeffective when applied before exposure to radiation or other mutagens,as long as the deoxyribonucleosides so provided, or their anabolites,are available to cells in need of their beneficial effects at the timeof exposure to a mutagen. Advantageously, compositions of the inventionare applied within about 12 hours before exposure of the skin to a solarradiation or other mutagens.

[0115] Compositions of the invention are advantageously applied as adaily-use skin treatment, once to several times per day, especially onsun-exposed parts of the body, or sites of inflammatory skin conditions.Exposure to solar radiation leading to skin photodamage and photoagingis generally a cumulative process, involving repeated exposure tosunlight, even daily, over a period of years. In this context, use ofthe compounds and compositions of the invention to prevent or treatphotodamage to the skin involves treatment of existing lesions due toprior sun exposure, as well as prevention of, or attenuation of theseverity of, damage due to present and future exposure to sunlight orother mutagens.

[0116] By improving repair of molecular damage to DNA as it occurs orbefore it is permanently established in the genome by cell division, orby preventing initial damage through energy scavenging, compositions ofthe invention prevent or delay the manifestation of deleteriousconsequences of radiation, free radicals, or chemical mutagens, such asgrossly visible skin damage, photoaging, actinic keratoses, and skincancer. Thus, compositions and methods of the invention reduce the rateof appearance and the incidence of signs of skin photodamage, especiallywhen administered regularly, e.g. daily, or especially before, during,or after exposure to solar radiation.

[0117] Compositions of the invention are also useful for promotingregression of established sunlight-induced and other inflammatory andhyperproliferative skin lesions, e.g. actinic keratoses, contactdermatitis, psoriasis, eczema, or acne, or skin cancers like melanoma,basal cell carcinoma, or squamous cell carcinoma. In such conditions,topical gels, creams, ointments or lotions are applied to the affectedareas once or twice per day as needed.

[0118] In one embodiment of the invention, a composition containingdeoxyribonucleosides is applied to skin prior to application of asunscreen, as an alternative to use of formulations containing bothconventional sunscreens and deoxyribonucleosides or related compounds ofthe invention.

[0119] For treatment of colon mucosal inflammation, e.g. inflammatorybowel disease, compositions of the invention are administered as asuppository or enema, approximately once per day according to clinicalneed. Volumes of 10 to 500 ml of a suitable enema composition containingdeoxyribonucleosides are suitable for treatment of inflammatory boweldisease, e.g. ulcerative colitis or Crohn's disease. For treatment ofmucositis in other parts of the gastrointestinal, such as the mouth,standard pharmaceutically acceptable vehicles for that route ofadministration are used, e.g. mouthwashes or adherent hydrocolloids.

[0120] F. Synthesis of the Compounds of the Invention

[0121] Deoxyribonucleosides, being constituents of DNA, are present inall living organisms, and can therefore in principle be extracted from avariety of sources. In practice, the most convenient biological sourcesat present are fish milt, which contains a relatively high concentrationof DNA. Fish milt sacs are homogenized, and the DNA therein is partiallypurified and treated with deoxyribonucleases and phosphatases to degradeit to the level of nucleosides, which are then purified bychromatography and recrystallization.

[0122] Since mixtures of deoxyribonucleosides are used in someembodiments of the invention, purified deoxyribonucleosides arerecombined in appropriate proportions. Alternatively,deoxyribonuclosides are not separated from each other duringpurification from other fish milt components (or other contaminants ifthe DNA is derived from other biological sources); appropropriatequantities of individual deoxyribonucleosides are added to such amixture, if necessary, to adjust the relative proportions ofdeoxyribonucleosides.

[0123] Deoxyribonucleosides can also be synthesized chemically fromsimpler precursors.

[0124] Acyl derivatives of deoxyribonucleosides, as disclosed in U.S.patent application Ser. No. 466,379, are useful for 1) providingsustained availability of deoxyribonucleosides due to gradualdeacylation by nonspecific esterases in the skin, and 2) improvedpenetration through hydrophobic biological membranes or extracellularmedia, e.g. the intercellular lipids in the stratum corneum of theepidermis.

[0125] It will be obvious to the person skilled in the art that othermethods of synthesis may be used to prepare the compounds of theinvention.

[0126] The following examples are illustrative, but not limiting of themethods and compositions of the present invention. Other suitablemodifications and adaptations of a variety of conditions and parametersnormally encountered in clinical therapy which are obvious to thoseskilled in the art are within the spirit and scope of this invention.

EXAMPLE 1

[0127] Post-irradiation topical deoxyribonucleosides improve DNA repairin mouse skin after UVB exposure The incidence of mutations in skin inresponse to ultraviolet radiation was determined using the “Big Blue”transgenic mouse test system. These mice carry approximately 40 copiesper cell of a lambda phage shuttle vector containing a ladI gene as atarget for mutagenesis, as well as the lacI promoter, the lac operator,and the αlacZ reporter gene.

[0128] Following exposure of the mice to ultraviolet radiation andtreatment with compounds of the invention or vehicle, genomic DNA fromskin samples is extracted and the shuttle vectors are packaged in lambdavirus heads. The phage lambda viruses containing the shuttle vectors areplated on E. Coli with the color reagent X-Gal, which turns blue whenenzymatically altered by galactosidase, the product of the αlacZ gene.Viruses containing nonmutated lacI genes produce white plaques; mutationof the lacI gene results in blue plaques. The mutation frequency isdetermined by counting the relative numbers of white and blue plaques.

[0129] Stratagene BigBlue™ transgenic mice (n=7/group) were shaved andthen irradiated the next day with UVB radiation (85% of energy at 313nm), 1.25 kJ/m2.

[0130] Deoxyribonucleosides (“dNsides”; 4 mg/ml each of deoxyadenosine,deoxycytidine, deoxyguanosine, and thymidine) or vehicle (propyleneglycol) were applied topically 30 minutes after irradiation and againeach day for 5 days.

[0131] Mice were sacrificed on day 5 after irradiation. DNA wasextracted from dorsal (irradiated) and ventral (non-irradiated) skin,packaged into lambda phage and plated on E. Coli along with X-Gal.Colonies with mutations were blue. >200,000 colonies were counted ineach group. TABLE 1 Topical deoxyribonucleosides reduce mutationfrequency in UV-irradiated skin Spontaneous mutation frequency(nonirradiated skin): Average:  4.5 × 10⁻⁵ Mutation frequency inUVB-irradiated skin: Total Increment due to UV Control 34.9 × 10⁻⁵ 30.4× 10⁻⁵ dNsides  7.8 × 10⁻⁵  3.3 × 10⁻⁵

[0132] As shown in Table 1, post-irradiation treatment with topicaldeoxyribonucleosides reduced the incidence of mutations caused by UV-Bradiation by a factor of nearly 10 in this experiment (30.4×10⁻⁵ versus3.3×10⁻⁵)

EXAMPLE 2

[0133] Post-irradiation Treatment with Topical DeoxyribonucleosidesPrevents Development of UV-induced Papillomas in v-Ha-ras TransgenicTG.AC Mice

[0134] Example 1 demonstrated that post-irradiation topical treatmentcan reduce the frequency of UV-induced mutations in a reporter gene in“Big Blue” transgenic mice, through support and improvement of DNArepair processes. One of the consequences of reduced mutation frequencyin response to a carcinogen like UV radiation should be a reduction ofUV-induced tumorigenesis.

[0135] A strain of transgenic mice has been developed which is extremelysensitive to carcinogens. It permits rapid determination of carcinogenicpotential of various chemical agents and other treatments. Normal micerequire repeated exposure to ultraviolet radiation over a number ofweeks in order to reliably develop skin tumors. In contrast, v-Ha-rasTG.AC transgenic mice can develop tumors rapidly after a singleexposure, or small number of exposures to UV radiation.

[0136] In 9 mice exposed to UV-B radiation (0.3-1.25 kJ/m² x3 q2d) andtreated after irradiation with vehicle (propylene glycol), a total of 35papillomas were found 4 weeks after exposure.

[0137] Among 7 mice exposed to the same doses of UV-B radiation andtreated with deoxyribonucleosides (4 mg/ml of each majordeoxyribonucleoside in propylene glycol) after irradiation, only 1papilloma was observed (Table 2). TABLE 2 Topical deoxyribonucleosidesreduce UV-induced tumorigenesis Control: 3.89 tumors/mousedNside-treated: 0.14 tumors/mouse

[0138] The beneficial effect of deoxyribonucleosides in reducingUV-induced tumorigenesis must be due to improvement of repair phenomenaor cellular proofreading, or to inhibition of tumor promotion, and notto prevention of initial damage, since the deoxyribonucleosides wereapplied after irradiation. This observation indicates thatdeoxyribonucleoside treatment after (or presumably also during) exposureto LWV-B radiation has important inhibitory effects on tumorigenesis, asa consequence of improved maintenance of genomic fidelity.

[0139] This antitumorigenic effect of topical deoxyribonucleosides evenwhen applied after irradiation is particularly surprising in view of thereported efficacy of deoxyribonucleosides in accelerating wound healing(U.S. Pat. No. 5,246,708), since other growth factors known toaccelerate wound healing, like platelet-derived growth factor (PDGF) ortransforming growth factor beta (TGF-B), act as tumor promoters.

[0140] The antitumorigenic effect of deoxyribonucleosides in thisexperiment is also unexpected in view of the beneficial effect ofdeoxyribonucleosides on survival of cells in culture when thedeoxyribonucleosides are applied after exposure of the cells toultraviolet or ionizing radiation. Prevention of apoptosis of damagedcells would be expected to increase the likelihood of tumor development,as occurs in animals with defective p53-related mechanisms.

EXAMPLE 3

[0141] Low Concentrations of Oxybenzone Exacerbate UTV-induced Damage toDNA

[0142] Confluent human fibroblasts in T25 flasks were washed 3 timeswith HBSS (Hank's Balanced Salt Solution) and incubated with vehicle orwith various concentrations of oxybenzone (OB) for 2 hours. Media wasaspirated and cells were covered with a 1 mm layer of HBSS andirradiated from above with UV-B (50 J/m²). The medium was aspirated andcells were incubated for three hours with 2 mM hydroxyurea. Medium wasagain aspirated, and cells were trypsinized with 0.25% trypsin/EDTA.Cells were centrifuged at 4° C., resuspended in 50 microliters of HBSSand incubated at room temperature with 200 microliters of 1N NaOH for 15minutes. DNA damage (single strand breaks) was assessed by alkalinesucrose gradient centrifugation. “Nucleoid position” in the sucrosegradient is proportional to the number of DNA single strand breaks.

[0143] UV irradiation without oxybenzone results in a three to four-foldincrease in the nucleoid position over baseline (Table 3). Oxybenzone atthe higher concentrations tested, 20 and 200 micromolar, protectedcellular DNA against damage from the UV irradiation, as the nucleoidposition for these groups is close to that of non-irradiated cells.However, cells exposed to 2 micromolar OB display substantially moredamage than cells irradiated with no OB at all; nucleoid position valuesare 10-fold greater than those of non-irradiated cells. Thus, oxybenzonestrongly enhances DNA damage when present at low concentrations, whereasit protects cells at higher concentrations. In practice, even underconditions of proper sunscreen use, there will always be areas of skinexposed to low, potentially deleterious concentrations of sunscreen,either at the edge of a patch of applied sunscreen, or as an appliedlayer wears off over the course of a day. TABLE 3 Low concentrations ofoxybenzone enhance UV-induced DNA damage Group Nucleoid Position (mm) NoUV 3 UV 50 J/m² 11 UV 50 J/m² + 2 μM OB 32 UV 50 J/m² + 20 μM OB 4 UV 50J/m² + 200 μM OB 3

EXAMPLE 4

[0144] Deoxribonucleosides Attenuate Photodynamic Enhancement of DNADamage Caused by Oxybenzone

[0145] Confluent human fibroblasts were exposed to 2 micromolaroxybenzone (OB), as in Example 3, prior to exposure to UV-B radiation(50 J/m²). Different flasks of cells also were exposed to increasingconcentrations of deoxyribonucleosides. Cells were processed fordetermination of nucleoid position in a sucrose density gradient, ameasure of DNA single strand breaks.

[0146] As shown in Table 4, deoxyribonucleosides produce adose-dependent reduction in the yield of DNA single strand breaksinduced by UV exposure plus 2 μM OB. Deoxyribonucleosides at 2 μMslightly reduce DNA damage; at 200 micromolar, the deoxyribonucleosidesalmost completely abrogate the DNA damage. TABLE 4 Deoxyribonucleosidesattenuate photodynamic enhancement of DNA damage caused by UV plusoxybenzone Group Nucleoid Position (mm) UV + 2 μM OB 56 UV + 2 μM OB + 2μM dNsides 47 UV + 2 μM OB + 20 μM dNsides 23 UV + 2 μM OB + 100 μMdNsides 22 UV + 2 μM OB + 200 μM dNsides 7

EXAMPLE 5

[0147] Effect of Individual Versus Combined Deoxribonucleosides onPhotodynamically-enhanced, UV-induced DNA Damage

[0148] Human fibroblasts were prepared and treated as in Example 4, andthe effects of individual deoxyribonucleosides on photodynamicallyenhanced DNA damage (2 μM oxybenzone) were determined. Individualdeoxyribonucleosides were tested at concentrations of 20 μM, and thecombination of all four deoxyribonucleosides contained thymidine,deoxycytidine, deoxyadenosine and deoxyguanosine at 20 μM each. TABLE 5Effect of individual versus combined deoxyribonucleosides on UV-inducedDNA damage DNA Strand Breaks Group (Breaks/47 MDa) Control (no UV) .0UV + vehicle .325 UV + thymidine .13 UV + deoxycytidine .12 UV +deoxyadenosine .17 UV + deoxyguanosine .17 UV + dNsides (20 μM each) .01

[0149] As shown in Table 5, each of the individual deoxyribonucleosidesattenuated DNA damage; the combination of all four deoxyribonucleosideswas substantially more effective than any individual compound.

EXAMPLE 6

[0150] Sunscreen-induced Exacerbation of UV-induced Tumorigenesis andits Prevention with Deoxyribonucleosides

[0151] A circular patch of commercial sunscreen (Coppertone SPF 8, whichincludes oxybenzone) was applied to the backs of TG.AC mice prior toexposure to 125 J/m² UV-B radiation.

[0152] Around the circular margin of the area that was covered withsunscreen during irradiation, 8 papillomas per mouse were present at 10days. 3 tumors per mouse were observed in animals not treated withsunscreen. In mice exposed to UV radiation after application of the samecommercial sunscreen to which deoxyribonucleosides had been added, nopapillomas were elicited (Table 6). TABLE 6 Deoxyribonucleosidesattenuate tumorigenesis in in mice treated with UV plus sunscreen UVRadiation 3 tumors/mouse Sunscreen + UV radiation: 8 tumors/mouseSunscreen containing dNsides + UV radiation: 0 tumors/mouse

[0153] Thus, at the margin of the applied patch of sunscreen where thesunscreen concentration diminishes in a rapid gradient toward zero,tumorigenic UV damage in fact appears to be enhanced rather than reducedby the sunscreen agents, leading to formation of more premalignantpapillomas than on skin not treated with sunscreen at all.

[0154] Addition of deoxyribonucleosides to a commercial sunscreenabrogated the deleterious effect of the sunscreen on tumorigenesis.

EXAMPLE 7

[0155] Effect of Individual Deoxyribonucleosides Versus a Combination onUV-induced Tumorigenesis

[0156] Thirty v-Ha-ras TG.AC mice aged twelve weeks were shaved andsubjected to ultraviolet radiation, 1.25 kJ/m² on days 0, 6, 8 and 11,at a dose rate of 12.5 W/m2.

[0157] Mice were divided into groups of five animals each and treated,beginning 30 minutes after irradiation, with:

[0158] 1. Vehicle (propylene glycol)

[0159] 2. dNsides—Deoxyribonucleosides (4 mg/ml each of deoxyadenosine,deoxycytidine, deoxyguanosine, and thymidine)

[0160] 3. dC—Deoxycytidine (4 mg/ml)

[0161] 4. dG—Deoxyguanosine (4 mg/ml)

[0162] 5. dA—Deoxyadenosine (4 mg/ml)

[0163] 6. dT—Thymidine (4 mg/ml)

[0164] Animals were observed for 8 weeks, during which time thedevelopment of papillomas was observed. TABLE 7 Effect of individualversus combined deoxyribonucleosides on UV-induced tumorigenesisPapillomas/mouse at the end of 8 weeks: Vehicle 1.8 dNsides 0.0 dC 0.25dG 1.0 dA 0.67 dT 1.6

[0165] As shown in Table 7, the mixture of all four deoxyribonucleosidesprovided the best activity in terms of prevention of tumor development.Deoxycytidine also provided protection; deoxyadenosine anddeoxyguanosine were less protective but nonetheless had activity.Thymidine did not have significant protective actions.

EXAMPLE 8

[0166] Nitric Oxide Causes and Enhances DNA Damage by aDeoxyribonucleoside-reversible Mechanism

[0167] Nitric oxide is a mediator of UV-induced erythema, and is alsopresent in inflammatory skin conditions. NO is mutagenic, and mayexacerbate UV-induced DNA damage, in part by inhibiting ribonucleotidereductase, the enzyme responsible for conversion of ribonucleotides todeoxyribonucleotides.

[0168] Human melanocytes were exposed to 160 μM DETA NONOate (AlexisCorporation, Cat # 430-014-M005), a reagent which spontaneously producesnitric oxide when exposed to water. Cells were exposed to NO alone, orNO plus increasing doses of UV radiation (50 and 300 J/m²). Groups ofcells were also exposed to deoxyribonucleosides of the invention before,or before and after, exposure to NO or NO+UV radiation; control groupswere treated identically except for addition of deoxyribonucleosides.

[0169] DNA was extracted from cells and subjected to pulsed field gelelectrophoresis to determine the incidence of DNA strand breaks.

[0170] As shown in Table 8, NO alone produced a significant incidence ofDNA strand breaks, which were further increased by exposure to UVradiation. The deoxyribonucleosides of the invention strongly reducedthe incidence of DNA strand breaks caused by NO, as well as those causedby the combination of NO plus UV radiation. TABLE 8 Deoxyribonucleosidesattenuate Nitric Oxide-induced DNA damage DNA Strand Breaks Groups(breaks/105 MDa) Control 0.00 NO 0.13 NO + UV 50 J/m² 0.21 NO + UV 300J/m² 0.51 NO + dNsides before and after UV 0.00 NO + UV 50 J/m² +dNsides before/after UV 0.03 NO + UV 300 J/m² + dNsides before/after UV0.03 NO + dNsides after UV 0.06 NO + UV 50 J/m² + dNsides after UV 0.06NO + UV 300 J/m² + dNsides after UV 0.03

EXAMPLE 9

[0171] Treatment of Existing Actinic Keratosis with TopicalDeoxyribonucleosides

[0172] Actinic keratosis (AK) is a form of intradermal neoplasia, asunlight-induced lesion which can progress to become squamous cellcarcinoma. A 46 year-old woman with very light skin presented with apersistent rose colored, rough-surfaced lesion 5×10 mm in size on herforehead. The lesion was diagnosed as an actinic keratosis by aboard-certified dermatologist, who prescribed topical 5-fluorouracil forits treatment. Since 5-fluororacil, a standard treatment for AK, canproduce pain and unsightly skin erosion which takes several weeks toheal and is also potentially genotoxic, the subject elected to first tryto treat the AK with topical deoxyribonucleosides (4 mg/ml each ofdeoxycytidine, deoxyadenosine, deoxyguanosine, and thymidine) in ahydrogel formulation, of which 0.1 ml was applied to the lesion twicedaily. Within 10 days, the AK on her forehead had begun to visiblyregress, and after three weeks, there was no trace of the AK, nor wasthere any scar or discomfort during or after treatment. 5-fluorouraciltreatment and other painful or invasive measures like excision orfreezing with liquid nitrogen were thus not needed. The AK has notrecurred after more than six months.

EXAMPLE 10

[0173] Formulation of a Composition of the Invention

[0174] A suitable clinical formulation of a composition of the inventioncomprises the following ingredients. The batch size is optionally scaledto any desired volume. 1. 2′-Deoxycytidine Hydrochloride 0.4640 g 2.2′-Deoxyadenosine Monohydrate 0.4290 g 3. 2′-Deoxyguanosine Monohydrate0.4270 g 4. Thymidine 0.4000 g 5. Edetate Disodium Dihydrate, USP 0.0100g 6. Benzethonium Chloride, USP 0.0250 g 7. Butylated Hydroxytoluene, NF0.0005 g 8. Carbomer 934P, NF 0.7200 g 9. Glycerin, USP 10.000 g 10.Alcohol, USP 5.000 g 11. Diethylene glycol monoethyl ether 10.000 g 12.NaOH, NF (1 N Solution) as needed for pH adjustment 13. HCl, NF (1 NSolution) as needed for pH adjustment 14. Purified Water, USP q.s. to100.00 g

[0175] Preparation:

[0176] 1. Item 8 (Carbomer 934P) is dissolved in 35 g of Purified Water.

[0177] 2. Item 5 is dissolved into the solution.

[0178] 3. Into a separate container, Items 9, 10, 11 are mixed with 15 gPurified Water.

[0179] 4. Items 1, 2, 3, 4, 6, and 7 are dissolved in the solution ofstep 3,

[0180] 5. The solutions of step 2 and 4 are mixed together.

[0181] 6. 8.85 g of Item 12 are added to the solution of step 5.

[0182] 7. The resulting gel is blended for 15 minutes, and the pH isadjusted to 7.0+/−0.5 with Item 12 or 13 as needed.

[0183] 8. The final weight of the batch is brought to 100 g withPurified Water followed by gentle blending for 15 minutes.

[0184] The foregoing is intended as illustrative of the presentinvention but not limiting. Numerous variations and modifications may beeffected without departing from the true spirit and scope of theinvention.

What is claimed is:
 1. A method of improving DNA repair in the skin ormucosa of a mammal comprising administering to said mammal at least onedeoxyribonucleoside, deoxyribonucleotide, or oligodeoxyribonucleotide.2. A method as in claim 1 wherein said at least one deoxyribonucleosideis administered topically.
 3. A method as in claim 1 wherein said atleast one deoxyribonucleoside is selected from the group consisting ofdeoxycytidine, deoxyadenosine, deoxyguanosine, and thymidine.
 4. Amethod as in claim 3 wherein said at least one deoxyribonucleoside isdeoxycytidine.
 5. A method as in claim 3 wherein said at least onedeoxyribonucleoside is deoxyadenosine.
 6. A method as in claim 3 whereinsaid at least one deoxyribonucleoside is deoxyguanosine.
 7. A method asin claim 3 wherein said at least one deoxyribonucleoside is thymidine.8. A method as in claim 3 wherein said at least one deoxyribonucleosideis administered in a vehicle containing from 0.1 to 10 milligrams permilliliter of each deoxyribonucleoside.
 9. A method as in claim 3wherein said at least one deoxyribonucleoside is administered in avehicle containing from 1.0 to 5 milligrams per milliliter of eachdeoxyribonucleoside.
 10. A method as in claim 3 wherein said at leastone deoxyribonucleoside is a mixture of deoxycytidine, deoxyadenosine,deoxyguanosine, and thymidine.
 11. A method as in claim 10 wherein saiddeoxyribonucleoside is administered in a vehicle containing from 0.1 to10 milligrams per milliliter of each deoxyribonucleoside.
 12. A methodas in claim 10 wherein said deoxyribonucleoside is administered in avehicle containing from 1 to 5 milligrams per milliliter of eachdeoxyribonucleoside.
 13. A method for reducing mutation frequency inskin of a mammal exposed to a mutagen comprising administering to saidskin a source of at least one deoxyribonucleoside.
 14. A method as inclaim 13 wherein said mutagen is selected from the group consisting ofultraviolet or solar radiation, a chemical mutagen, a free radical, orionizing radiation.
 15. A method as in claim 13 wherein said source isselected from the group consisting of at least one free or acyldeoxyribonucleoside.
 16. A method as in claim 13 wherein said source isselected from the group consisting of a deoxyribonucleotide, anoligodeoxyribonucleotide, and a polydeoxyribonucleotide.
 17. A method asin claim 13 wherein said source of at least one deoxyribonucleoside isadministered in a vehicle at a concentration of from 1.0 to 20milligrams per milliliter.
 18. A method as in claim 15 wherein said atleast one deoxyribonucleoside is free or acyl deoxycytidine.
 19. Amethod as in claim 15 wherein said at least one deoxyribonucleoside isfree or acyl deoxyadenosine.
 20. A method as in claim 15 wherein said atleast one deoxyribonucleoside is free or acyl deoxyguanosine.
 21. Amethod as in claim 15 wherein said at least one deoxyribonucleoside isfree or acyl thymidine.
 22. A method as in claim 15 wherein said atleast one deoxyribonucleoside is administered in a vehicle containingfrom 0.1 to 10 milligrams per milliliter of each deoxyribonucleoside.23. A method as in claim 15 wherein said at least onedeoxyribonucleoside is administered in a vehicle containing from 1.0 to5 milligrams per milliliter of each deoxyribonucleoside.
 24. A method asin claim 15 wherein said at least one deoxyribonucleoside is a mixtureof free or acyl deoxycytidine, deoxyadenosine, deoxyguanosine, andthymidine.
 25. A method as in claim 24 wherein said at least onedeoxyribonucleoside is administered in a vehicle containing from 0.1 to10 milligrams per milliliter of each deoxyribonucleoside.
 26. A methodas in claim 24 wherein said at least one deoxyribonucleoside isadministered in a vehicle containing from 1 to 5 milligrams permilliliter of each deoxyribonucleoside.
 27. A method for reducing thechance of developing skin cancer in a mammal due to exposure to amutagen comprising administering to the skin of said mammal a source ofat least one deoxyribonucleoside wherein said source is administeredsuch that said at least one deoxyribonucleoside is present on skin ofsaid mammal during or after exposure to said mutagen in an amountsufficient to reduce the deleterious consequences of said exposure. 28.A method as in claim 27 wherein said source is administered within 3days after exposure to a mutagen.
 29. A method as in claim 28 whereinsaid mutagen is selected from the group consisting of solar,ultraviolet, or ionizing radiation.
 30. A method as in claim 27 whereinsaid source is selected from the group consisting of at least one freeor acyl deoxyribonucleoside.
 31. A method as in claim 27 wherein saidsource is selected from the group consisting of a deoxyribonucleotide,an oligodeoxyribonucleotide, and a polydeoxyribonucleotide.
 32. A methodas in claim 27 wherein said source of at least one deoxyribonucleosideis administered in a vehicle at a concentration of from 1.0 to 20milligrams per milliliter.
 33. A method as in claim 30 wherein said atleast one deoxyribonucleoside is free or acyl deoxycytidine.
 34. Amethod as in claim 30 wherein said at least one deoxyribonucleoside isfree or acyl deoxyadenosine.
 35. A method as in claim 30 wherein said atleast one deoxyribonucleoside is free or acyl deoxyguanosine.
 36. Amethod as in claim 30 wherein said at least one deoxyribonucleoside isfree or acyl thymidine.
 37. A method as in claim 30 wherein said atleast one deoxyribonucleoside is administered in a vehicle containingfrom 0.1 to 10 milligrams per milliliter of each deoxyribonucleoside.38. A method as in claim 30 wherein said at least onedeoxyribonucleoside is administered in a vehicle containing from 1.0 to5 milligrams per milliliter of each deoxyribonucleoside.
 39. A method asin claim 30 wherein said at least one deoxyribonucleoside is a mixtureof free or acyl deoxycytidine, deoxyadenosine, deoxyguanosine, andthymidine.
 40. A method as in claim 39 wherein said at least onedeoxyribonucleoside is administered in a vehicle containing from 0.1 to10 milligrams per milliliter of each deoxyribonucleoside.
 41. A methodas in claim 39 wherein said at least one deoxyribonucleoside isadministered in a vehicle containing from 1 to 5 milligrams permilliliter of each deoxyribonucleoside.
 42. A method as in claim 27wherein said skin cancer is selected from the group comprising basalcell carcinoma, melanoma, and squamous cell carcinoma.
 43. A method forreducing the rate of skin photoaging in a mammal comprisingadministering to the skin of said mammal at least onedeoxyribonucleoside.
 44. A method as in claim 43 wherein said at leastone deoxyribonucleoside is deoxycytidine.
 45. A method as in claim 43wherein said at least one deoxyribonucleoside is deoxyadenosine.
 46. Amethod as in claim 43 wherein said at least one deoxyribonucleoside isdeoxyguanosine.
 47. A method as in claim 43 wherein said at least onedeoxyribonucleoside is thymidine.
 48. A method as in claim 43 whereinsaid at least one deoxyribonucleoside is administered in a vehiclecontaining from 0.1 to 10 milligrams per milliliter of eachdeoxyribonucleoside.
 49. A method as in claim 43 wherein said at leastone deoxyribonucleoside is administered in a vehicle containing from 1.0to 5 milligrams per milliliter of each deoxyribonucleoside.
 50. A methodas in claim 43 wherein said at least one deoxyribonucleoside is amixture of deoxycytidine, deoxyadenosine, deoxyguanosine, and thymidine.51. A method as in claim 50 wherein said at least onedeoxyribonucleoside is administered in a vehicle containing from 0.1 to10 milligrams per milliliter of each deoxyribonucleoside.
 52. A methodas in claim 50 wherein said at least one deoxyribonucleoside isadministered in a vehicle containing from 1 to 5 milligrams permilliliter of each deoxyribonucleoside.
 53. A method for reducing thechance of developing actinic keratoses in a mammal comprisingadministering to the skin of said mammal a source of at least onedeoxyribonucleoside.
 54. A method as in claim 53 wherein said source isselected from the group consisting of a deoxyribonucleoside, adeoxyribonucleotide, an oligodeoxyribonucleotide, and an acylderivatives of deoxyribonucleoside.
 55. A method of reducing thedeleterious consequences of photosensitization or photodynamicsensitization on the skin of a mammal caused by an endogenous orexogenous photochemically active chromophore comprising administering tosaid skin an energy scavenging agent with a lowest triplet state energyless than or equal to that of nucleobases in DNA.
 56. A method as inclaim 55 wherein said exogenous chromophore is a sunscreen agent.
 57. Amethod as in claim 56 wherein said sunscreen agent is selected from thegroup consisting of avobenzone (t-butyl dimethoxydibenzoylmethane),oxybenzone (benzophenone-3), dioxybenzone (benzophenone-8),sulisobenzone (benzophenone-4;2-hydroxy-4-methoxybenzophenone-5-sulfonic acid), octocrylene(2-ethylhexyl-2-cyano-3,3-diphenylacrylate), octyl methoxycinnamate(2-ethylhexyl p-methoxycinnamate), octyl salicylate(2-ethylhexylsalicylate), homosalate (homomenthyl salicylate), trolaminesalicylate (triethanolamine salicylate), phenylbenzimidazole sulfonicacid, PABA (para-aminobenzoic acid), roxadimate (ethyl 4-bishydroxypropyl aminobenzoate), lisadimate (glyceryl PABA), Padimate O(octyldimethyl PABA), menthyl anthranilate, or Parsol 1789 (butylmethoxydibenzoylmethane)
 58. A method as in claim 55 wherein said energyscavenging agent is selected from the group consisting of DNA, anoligodeoxyribonucleotide, a ribonucleoside, a deoxyribonucleoside, aribonucleotide, a deoxyribonucleotide, an acyl deoxyribonucleoside, andan acyl ribonucleoside.
 59. A method as in claim 58 wherein said energyscavenging agent is administered in a vehicle containing 0.1 to 20mg/ml.
 60. A method as in claim 58 wherein said energy scavenging agentis a mixture comprising free or acylated deoxycytidine, deoxyadenosine,deoxyguanosine, and thymidine.
 61. A method as in claim 60 wherein saidmixture is administered in a vehicle containing from 0.1 to 10milligrams per milliliter of each deoxyribonucleoside.
 62. A method forreducing the deleterious consequences of exposure of a mutagen to theskin of a mammal comprising administering to said mammal at least onedeoxyribonucleoside, deoxyribonucleotide, or oligodeoxyribonucleotide.63. A method as in claim 62 wherein said mutagen is solar or ultravioletradiation.
 64. A method as in claim 62 wherein said mutagen is ionizingradiation.
 65. A method as in claim 62 wherein said mutagen is a freeradical.
 66. A method as in claim 62 wherein said at least onedeoxyribonucleoside is administered topically.
 67. A method as in claim62 wherein said at least one deoxyribonucleoside is selected from thegroup consisting of deoxycytidine, deoxyadenosine, deoxyguanosine, andthymidine.
 68. A method as in claim 67 wherein said at least onedeoxyribonucleoside is deoxycytidine.
 69. A method as in claim 67wherein said at least one deoxyribonucleoside is deoxyadenosine.
 70. Amethod as in claim 67 wherein said at least one deoxyribonucleoside isdeoxyguanosine.
 71. A method as in claim 67 wherein said at least onedeoxyribonucleoside is thymidine.
 72. A method as in claim 67 whereinsaid at least one deoxyribonucleoside is administered in a vehiclecontaining from 0.1 to 10 milligrams per milliliter of eachdeoxyribonucleoside.
 73. A method as in claim 67 wherein said at leastone deoxyribonucleoside is administered in a vehicle containing from 1.0to 5 milligrams per milliliter of each deoxyribonucleoside.
 74. A methodas in claim 67 wherein said at least one deoxyribonucleoside is amixture of deoxycytidine, deoxyadenosine, deoxyguanosine, and thymidine.75. A method as in claim 74 wherein said deoxyribonucleoside isadministered in a vehicle containing from 0.1 to 10 milligrams permilliliter of each deoxyribonucleoside.
 76. A method as in claim 74wherein said deoxyribonucleoside is administered in a vehicle containingfrom 1 to 5 milligrams per milliliter of each deoxyribonucleoside.
 77. Amethod of reducing the deleterious consequences of exposure of skin toendogenously produced nitric oxide comprising administering to said skina source of at least one deoxyribonucleoside.
 78. A method as in claim77 wherein said source of at least one deoxyribonucleoside is selectedfrom the group consisting of a deoxyribonucleoside, adeoxyribonucleotide, an oligodeoxyribonucleotide, or an acyldeoxyribonucleoside.
 79. A method as in claim 77 wherein said source ofat least one deoxyribonucleoside is administered in a vehicle at aconcentration of from 1.0 to 20 milligrams per milliliter.
 80. A methodas in claim 78 wherein said at least one deoxyribonucleoside is free oracyl deoxycytidine.
 81. A method as in claim 78 wherein said at leastone deoxyribonucleoside is free or acyl deoxyadenosine.
 82. A method asin claim 78 wherein said at least one deoxyribonucleoside is free oracyl deoxyguanosine.
 83. A method as in claim 78 wherein said at leastone deoxyribonucleoside is free or acyl thymidine.
 84. A method as inclaim 78 wherein said at least one deoxyribonucleoside is administeredin a vehicle containing from 0.1 to 10 milligrams per milliliter of eachdeoxyribonucleoside.
 85. A method as in claim 78 wherein said at leastone deoxyribonucleoside is administered in a vehicle containing from 1.0to 5 milligrams per milliliter of each deoxyribonucleoside.
 86. A methodas in claim 78 wherein said at least one deoxyribonucleoside is amixture of free or acyl deoxycytidine, deoxyadenosine, deoxyguanosine,and thymidine.
 87. A method as in claim 86 wherein said at least onedeoxyribonucleoside is administered in a vehicle containing from 0.1 to10 milligrams per milliliter of each deoxyribonucleoside.
 88. A methodas in claim 86 wherein said at least one deoxyribonucleoside isadministered in a vehicle containing from 1 to 5 milligrams permilliliter of each deoxyribonucleoside.
 89. A method of treating skininflammation in a mammal comprising administering to inflamed skin asource of at least one deoxyribonucleoside or ribonucleoside.
 90. Amethod as in claim 89 wherein said skin inflammation is selected fromthe group consisting of dermatitis, psoriasis, eczema, and acne.
 91. Amethod as in claim 89 wherein said skin inflammation is due to exposureto solar or ultraviolet radiation.
 92. A method as in claim 89 whereinsaid source of at least one deoxyribonucleoside or ribonucleoside isselected from the group consisting of DNA, an oligodeoxyribonucleotide,a ribonucleoside, a deoxyribonucleoside, a ribonucleotide, adeoxyribonucleotide, an acyl deoxyribonucleoside, and an acylribonucleoside.
 93. A method as in claim 92 wherein said source of atleast one deoxyribonucleoside or ribonucleoside is administered in avehicle containing from 0.1 to 20 mg/ml.
 94. A method as in claim 92wherein said source of at least one deoxyribonucleoside is a mixturecomprising free or acylated deoxycytidine, deoxyadenosine,deoxyguanosine, and thymidine.
 95. A method as in claim 89 wherein saidsource of at least one deoxyribonucleoside is deoxycytidine.
 96. Amethod as in claim 89 wherein said source of at least one ribonucleosideis adenosine.
 97. A method as in claim 89 wherein said adenosine isadministered in a vehicle containing from 0.1 to 10 mg/ml.
 98. A methodof treating mucosal inflammation in a mammal comprising administering tosaid mucosal inflammation a source of at least one deoxyribonucleosideor ribonucleoside.
 99. A method as in claim 98 wherein said mucosal skininflammation is selected from the group consisting of inflammatory boweldisease, ulcerative colitis, Crohn's disease, stomatitis or mucositis.100. A method as in claim 98 wherein said source of at least onedeoxyribonucleoside or ribonucleoside is selected from the groupconsisting of DNA, an oligodeoxyribonucleotides, a ribonucleoside, adeoxyribonucleoside, a ribonucleotide, a deoxyribonucleotide, an acyldeoxyribonucleoside, and an acyl ribonucleoside.
 101. A method as inclaim 100 wherein said source of at least one deoxyribonucleoside isadministered in a vehicle containing from 0.1 to 20 mg/ml.
 102. A methodas in claim 100 wherein said source of at least one deoxyribonucleosideis a mixture comprising free or acylated deoxycytidine, deoxyadenosine,deoxyguanosine, and thymidine.
 103. A method as in claim 98 wherein saidsource of at least one deoxyribonucleoside is deoxycytidine.
 104. Amethod of reducing the chance of developing skin cancer in a mammal dueto exposure to solar or ultraviolet radiation comprising topicallyadministering a composition comprising a sunscreen agent and an energyscavenging agent.
 105. A method as in claim 104 wherein said sunscreenagent is selected from the group consisting of avobenzone (t-butyldimethoxydibenzoylmethane), oxybenzone (benzophenone-3), dioxybenzone(benzophenone-8), sulisobenzone (benzophenone4;2-hydroxy4-methoxybenzophenone-5-sulfonic acid), octocrylene(2-ethylhexyl-2-cyano-3,3-diphenylacrylate), octyl methoxycinnamate(2-ethylhexyl p-methoxycinnamate), octyl salicylate(2-ethylhexylsalicylate), homosalate (homomenthyl salicylate), trolaminesalicylate (triethanolamine salicylate), phenylbenzimidazole sulfonicacid, PABA (para-aminobenzoic acid), roxadimate (ethyl 4-bishydroxypropyl aminobenzoate), lisadimate (glyceryl PABA), Padimate O(octyldimethyl PABA), menthyl anthranilate, or Parsol 1789 (butylmethoxydibenzoylmethane)
 106. A method as in claim 104 wherein saidenergy scavenging agent is selected from the group consisting of DNA, anoligodeoxyribonucleotide, a ribonucleoside, a deoxyribonucleoside, aribonucleotide, a deoxyribonucleotide, an acyl deoxyribonucleoside, andan acyl ribonucleoside.
 107. A method as in claim 106 wherein saidenergy scavenging agent is administered in a vehicle containing from 0.1to 20 mg/ml.
 108. A method as in claim 106 wherein said energyscavenging agent is a mixture comprising free or acylated deoxycytidine,deoxyadenosine, deoxyguanosine, and thymidine.
 109. A compositioncomprising a) at least one deoxyribonucleoside and b) an agent thatenhances penetration of said at least one deoxyribonucleoside into theskin.
 110. A composition as in claim 109 wherein said skin is humanskin.
 111. A composition as in claim 109 wherein said at least onedeoxyribonucleoside is deoxycytidine.
 112. A composition as in claim 109wherein said source of at least one deoxyribonucleoside isdeoxyadenosine.
 113. A composition as in claim 109 wherein said sourceof at least one deoxyribonucleoside is deoxyguanosine.
 114. Acomposition as in claim 109 wherein said source of at least onedeoxyribonucleoside is thymidine.
 115. A composition as in claim 109wherein said at least one deoxyribonucleoside is present in aconcentration of from 0.1 to 10 milligrams per milliliter of eachdeoxyribonucleoside.
 116. A composition as in claim 109 wherein said atleast one deoxyribonucleoside is present in a concentration of from 1.0to 5 milligrams per milliliter of each deoxyribonucleoside.
 117. Acomposition as in claim 109 wherein said at least onedeoxyribonucleoside is a mixture comprising free deoxycytidine,deoxyadenosine, deoxyguanosine, and thymidine.
 118. A composition as inclaim 117 wherein each deoxyribonucleoside is present in a concentrationof 0.1 to 10 milligrams per milliliter.
 119. A composition as in claim117 wherein each deoxyribonucleoside is present in a concentration of 1to 5 milligrams per milliliter.
 120. A composition as in claim 109wherein said agent that enhances penetration is selected from the groupconsisting of ethanol, isopropanol, azone(1-dodecylazacycloheptan-2-one), oleic acid, linoleic acid, propyleneglycol, hypertonic glycerol, lactic acid, glycolic acid, citric acid,malic acid, and diethylene glycol monoethyl ether.
 121. A composition asin claim 120 wherein said agent that enhances penetration is diethyleneglycol monoethyl ether.
 122. A composition as in claim 121 wherein saiddiethylene glycol monoethyl ether is present in a concentration of 2 to20%.
 123. A composition as in claim 121 wherein said diethylene glycolmonoethyl ether is present in a concentration of 5 to 15%.
 124. Acomposition as in claim 109 wherein said composition is a hydrogel. 125.A composition as in claim 124 wherein the gelling agent for saidhydrogel is selected from the group consisting of methylcellulose,carboxymethylcellulose, hydroxypropylmethylcellulose, carbomer, Hypan,polyacrylate, and glycerine polyacrylate.
 126. A composition as in claim124 wherein the gelling agent for said hydrogel is carbomer.
 127. Acomposition as in claim 126 wherein the concentration of said carbomeris 2 to 10%.
 128. A composition comprising a) deoxyguanosine anddeoxyadenosine and b) benzyl alcohol.
 129. A composition as in claim 128wherein the concentration of said benzyl alcohol is between 0.1 and 5%.130. A composition as in claim 128 wherein the concentrations ofdeoxyguanosine and deoxyadenosine are between 0.1 and 10 mg/ml.
 131. Acomposition as in claim 128 further containing deoxycytidine andthymidine.
 132. A composition as in claim 131 wherein the concentrationsof deoxycytidine and thymidine are between 0.1 and 10 mg/ml.
 133. Acomposition comprising a methylxanthine and source of at least onedeoxyribonucleoside.
 134. A composition as in claim 133 wherein saidsource of at least one deoxyribonucleoside is selected from the groupconsisting of at least one deoxyribonucleoside and at least one acylderivative of a deoxyribonucleoside.
 135. A composition comprising a) asunscreen agent b) an energy scavenging agent.
 136. A composition as inclaim 135 wherein said sunscreen agent is selected from the groupconsisting of avobenzone (t-butyl dimethoxydibenzoylmethane), oxybenzone(benzophenone-3), dioxybenzone (benzophenone-8), sulisobenzone(benzophenone-4; 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid),octocrylene (2-ethylhexyl-2-cyano-3,3-diphenylacrylate), octylmethoxycinnamate (2-ethylhexyl p-methoxycinnamate), octyl salicylate(2-ethylhexylsalicylate), homosalate (homomenthyl salicylate), trolaminesalicylate (triethanolamine salicylate), phenylbenzimidazole sulfonicacid, PABA (para-aminobenzoic acid), roxadimate (ethyl 4-bishydroxypropyl aminobenzoate), lisadimate (glyceryl PABA), Padimate O(octyldimethyl PABA), menthyl anthranilate, and Parsol 1789 (butylmethoxydibenzoylmethane).
 137. A composition as in claim 135 whereinsaid energy scavenging agent is selected from the group consisting of asource of at least one deoxyribonucleoside.
 138. A composition as inclaim 137 wherein said source of at least one deoxyribonucleoside isselected from the group consisting of a deoxyribonucleoside, adeoxyribonucleotide, an oligodeoxyribonucleotide, or an acyldeoxyribonucleoside.
 139. A composition as in claim 138 wherein said atleast one deoxyribonucleoside is a mixture comprising free or acylateddeoxycytidine, deoxyadenosine, deoxyguanosine, and thymidine.
 140. Acomposition as in claim 138 wherein each deoxyribonucleoside is presentin a concentration of from 0.1 to 10 milligrams per milliliter.
 141. Acomposition as in claim 138 wherein said at least onedeoxyribonucleoside is free or acyl deoxycytidine.
 142. A composition asin claim 141 wherein said free or acyl deoxycytidine is present in aconcentration of from 0.1 to 100 milligrams per milliliter.
 143. Acomposition as in claim 135 wherein said energy scavenging agent isselected from the group consisting of a source of at least oneribonucleoside.
 144. A composition as in claim 143 wherein said sourceof at least one deoxyribonucleoside is selected from the groupconsisting of a ribonucleoside, a ribonucleotide, anoligoribonucleotide, or an acyl ribonucleoside.
 145. A method forreducing the rate of development of skin photodamage in a mammal exposedto solar or ultraviolet radiation comprising administering to the skinof said mammal a source of at least one deoxyribonucleoside wherein saidsource is administered such that said deoxyribonucleoside is present onskin of said mammal during or after exposure to said radiation in anamount sufficient to reduce the deleterious consequences of saidexposure.
 146. A method as in claim 145 wherein said source is selectedfrom the group consisting of at least one free or acyldeoxyribonucleoside.
 147. A method as in claim 145 wherein said sourceis selected from the group consisting of a deoxyribonucleotide, anoligodeoxyribonucleotide, and a polydeoxyribonucleotide.
 148. A methodof reducing the rate of development of skin photodamage in a mammal dueto exposure to solar or ultraviolet radiation comprising topicallyadministering a composition comprising a sunscreen agent and an energyscavenging agent.
 149. A method as in claim 148 wherein said energyscavenging agent is selected from the group consisting of DNA, anoligodeoxyribonucleotide, a ribonucleoside, a deoxyribonucleoside, aribonucleotide, a deoxyribonucleotide, an acyl deoxyribonucleoside, andan acyl ribonucleoside.
 150. A method for inducing regression ofinflammatory or hyperproliferative skin lesions due to exposure to solaror ultraviolet radiation comprising topically administering acomposition comprising a source of at least one deoxyribonucleoside ordeoxyribose.
 151. A method as in claim 150 wherein said skin lesion isselected from the group comprising actinic keratosis, solar lentigines,psoriasis, dermatitis, eczemea, melanoma, basal cell carcinoma, andsquamous cell carcinoma.
 152. A method as in claim 150 wherein saidsource of at least one deoxyribonucleoside is selected from the groupconsisting of a deoxyribonucleoside, a deoxyribonucleotide, anoligodeoxyribonucleotide, or an acyl deoxyribonucleoside.
 153. A methodas in claim 152 wherein said at least one deoxyribonucleoside is amixture comprising free or acylated deoxycytidine, deoxyadenosine,deoxyguanosine, and thymidine.
 154. A method as in claim 152 whereineach deoxyribonucleoside is present in a concentration of from 0.1 to 10milligrams per milliliter.
 155. A method as in claim 152 wherein said atleast one deoxyribonucleoside is free or acyl deoxycytidine.
 156. Amethod as in claim 155 wherein said free or acyl deoxycytidine ispresent in a concentration of from 0.1 to 100 milligrams per milliliter.157. A method as in claim 150 wherein said deoxyribose is present in atopical formulation in a concentration of 0.1 to 100 millimolar.